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Magnetic Flux Of Solenoid

(a) If the current in the solenoid is 2. If there is a solenoid of length L , radius R, number of turns N immersed in uniform magnetic field B with axis of the solenoid being parallel to the field, then what will be the flux linkage and the. The data was recorded in the table below, and plotted in the graph on the right. It is used for producing magnetic field. By Lenz's law, the e. For example, if the magnetic field lines penetrate the area head on (that is,. (a) Find the magnetic flux through the solenoid. How many turns should a coil wrapped around the outside of the solenoid have so that the emf induced in the coil is 15. Usually given the symbol H. •A changing MAGNETIC FLUX will generate a voltage (EMF –electromotive force) •Faraday 1831, Joseph Henry 1832 •EMF (voltage, potential) = -d B /dt = - (time rate of change of magnetic flux) Left –Faraday’s disk –rotating a metal disk in a stationary magnetic field yields a DC current. Solenoids can convert electric current to mechanical action, and so are very commonly used as switches. The inductance of a solenoid is close to L=μr²n²π/l, but diverges increasingly from this estimation as the length becomes shorter relative to the radius. Let's assume that we have an ideal solenoid, in which case the magnetic field inside is B = m 0 nI, and the flux through the solenoid is F = BA = m 0 nIA, where A is the cross-sectional area of the solenoid. The test lamp responds to all kinds of magnetic fields, from alternating current to direct current and permanent magnets. Purpose: In this activity you will be looking at the circumstances under which a current will flow in a coil of wires. We have already shown that for an air-cored solenoid (section 4. The Magnetic Field of a Solenoid Magnetic Flux and Gauss's Law Faraday's Law of Induction. B=\frac {F} {Il} Where, l =length of wire F =total force acting on the wire I =current flowing through the wire. A solenoid is in an upright position on a table. In a solenoid, the core material is ferromagnetic, meaning that it concentrates magnetic lines of flux. 01256 T and magnetic flux = 1. - A current (I) in solenoid sets up B along its axis, the magnetic flux is: Induced current in loop (I'): I' = ε/ R - The force that makes the charges move around the loop is not a magnetic force. The current is analogous to the TOTAL flux Phi [Webers], and the current density will then be analogous to flux density B [Webers / sq m] The emf (is the Electro-Motive-Force) measured in [volts], and is analogous to the mmf (Magneto-Motive-Forc e) measured in [AmpTurns], H is the [AmpTurns per meter] around the magnetic circuit. 78 \times 10^{-4} {/eq} T{eq}\cdot {/eq}m{eq. Such coils, called solenoids, have an enormousnumber of practical applications. The best fit line through the data is also drawn. The soft-magnetic stainless steel part of the solenoid which is moved by magnetic forces (flux generated by the coil). Find the magnetic flux through the solenoid. A number of factors limit the upper bound of magnet flux density. The test lamp responds to all kinds of magnetic fields, from alternating current to direct current and permanent magnets. flux: The rate of transfer of energy (or another physical quantity) through a given surface, specifically electric flux or magnetic flux. Figure 23–3 The magnetic flux through a loop! The magnetic flux through a loop of area A is Φ= BA cosη, where ηis the angle between the normal to the loop and the magnetic field. Let's assume that we have an ideal solenoid, in which case the magnetic field inside is B = m 0 nI, and the flux through the solenoid is F = BA = m 0 nIA, where A is the cross-sectional area of the solenoid. Core form of solenoid: A solenoid is a basic device, which is used to provide an electromagnetic path in order to transmit maximum magnetic flux density with minimum input of energy. It is otherwise known as the magnetic field strength. The magnetic flux inside a solenoid is uniform. Figure 23-3 The magnetic flux through a loop! The magnetic flux through a loop of area A is Φ= BA cosη, where ηis the angle between the normal to the loop and the magnetic field. 0 T magnetic field pointing into the paper. The Experiment. Magnetic circuit is a method using an analogy with electric circuits to calculate the flux of complex systems of magnetic components. Browse other questions tagged solenoid magnetic-flux or ask your own question. (a) If the current in the solenoid is 2. Magnetic force between armature and stator pole can be calculated by Maxwell Tensile Force (see also Chap. Find the magnetic flux density and the total magnetic flux produced within the solenoid. Linear solenoid’s basically consist of an electrical coil wound around a cylindrical tube with a ferro-magnetic actuator or “plunger” that is free to move or slide “IN” and “OUT” of the coils body. Hazard Risk Control measure; Electrical. Magnetic Flux density is a measure of the strength of a magnetic field and is essentially how dense the field lines of a magnetic field are within a given height. (a) When there is a relative motion between the coil and the magnet, the magnetic flux linked with the coil changes. - If B is uniform: ΦB = B⊥ A = BA cos ϕ ΦB = ∫B⋅dA = 0 Units : 1 Weber (1 Wb = 1 T m 2 = 1 N m / A) - Difference with respect to electric flux the total magnetic flux through a closed surface is always zero. Each magnetic flux line is closed loop. Whereas, the magnetic flux shows the quantities of the magnetic lines of force passes through it. Induced emf is the rate of change magnetic flux. The higher the number, the better the shield. Successive-PFM processes in various pre-shaped magnetic flux distributions It is reported that the remnant trapped field distributions affects the successive magnetic flux application and their field-trapping behaviours [18, 19]. Permanent Magnet (PM) latching solenoid actuators utilize permanent magnets in conjunction with the solenoid coil to maintain the position of the armature with no current applied. 78 \times 10^{-4} {/eq} T{eq}\cdot {/eq}m{eq. The magnetic flux through a loop might change for a variety of reasons, but in this experiment we will only be concerned with the effect of a sinusoidally varying current in a nearby circuit. The magnetic field due to solenoid 1 passes (entirely, in this case) through solenoid 2, which has turns per unit length. The soft-magnetic stainless steel part of the solenoid which is moved by magnetic forces (flux generated by the coil). One side of the square is parallel to the conductor with distance of 4 cm between the side and the conductor. The shape of the magnetic flux lines. For the following scenarios, determine whether the magnetic flux changes or stays the same. The term solenoid refers specifically to. Calculate: A. Electromagnetism index. This is true for inductors in general. Eddy Currents. When properly applied, MFL can detect the presence and location of significant longitudinally or transversely oriented discontinuities such as pits, scabs, slivers, gouges, roll-ins, laps, seams, cracks, holes. The self-inductance of the solenoid isa)4. If the current in the solenoid is I = amperes. (a) What is the magnetic flux through one turn of a solenoid of self-inductance 8. 4 cm and 400 turns. Solenoid properties. We can calculate the flux by using: the region of area (A), the normal to which lies at an angle(𝜽) , and field of flux density (B), to get the equation 𝝓= 𝐜 𝐬𝜽 The unit of the magnetic flux is the weber (Wb. The inductance of the coil is. Investigation of magnetic flux density using a Hall probe. Hazard Risk Control measure; Electrical. For multiple loops of wire like in a solenoid, we use the quantity N φ. Magnetic fields are created by a electric current. 5 cm long and wound with 104 turns of wire. 2? We can build the solenoid with the larger cross-sectional area, 2*A, out of two solenoids with the initial cross-sectional area, A. The magnetic field inside the solenoid is directly proportional to the current flowing in the solenoid and the no. Symmetry properties of the cylinder and the judicious use of Ampere's circuital law leads to correct results; however it does not explain why the field is non zero for a. Current carried by the solenoid changes from 2 A to 4 A. Magnetic field strength is defined as the force acting per unit current in a wire of unit length, which is perpendicular to the field. Learn what magnetic flux means and how to calculate it. 008 m The magnetic flux through an annulus shaped solenoid -rl -(0 004m)2) Step 3 of 5. 2 m in diameter is 1. across a solenoid when the windings of the solenoid are cut by magnetic flux. solenoid, magnetic flux through square loop? A square, single-turn wire loop script l = 1. Magnetic flux linkage ʌ is total magnetic liking flux in a circuit. Find the magnetic flux through the loop when (a) L = 3. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Solenoids are available in a variety of formats; the two more common types are the linear solenoid and the rotary solenoid. Linear solenoid’s basically consist of an electrical coil wound around a cylindrical tube with a ferro-magnetic actuator or “plunger” that is free to move or slide “IN” and “OUT” of the coils body. When a current passes through it, it creates a nearly uniform magnetic field inside. The unit of magnetic induction is the tesla (T). The magnetic circuit shown in Fig. When a current passes through it, it creates a nearly uniform magnetic field inside. For instance, consider a 1 Coulomb (C) charge traveling at 100 meters per second (m/s) through the magnetic field of a solenoid with 1000 turns and 2 amperes (A) of current running through it. Presence of a flux return brings fringe magnetic field on the wall to the level of ~2. Magnetic Measurements and Faraday's Law. The magnetic flux (often denoted φ or φ B) through a surface is the component of the magnetic field passing through that surface. FIELD DUE TO SOLENOID When a current is passed through a solenoid the magnetic field is produced, which is strong and uniform inside, while it is negligibly weak outside. It becomes clear that magnetic flux decreases when residual magnetization is accounted when compared to when it isn’t accounted for. Some magnetic flux appears outside the coil (near ends of the core) and a small amount of flux flows off across the coil. It is otherwise known as the magnetic field strength. 2 m in diameter is 1. magnetic flux. Longitudinal magnetization of a component can be accomplished using the longitudinal field set up by a coil or solenoid. Hint: = 0 ( )I = 0 nI (22−12) L N B μ μ WhereWhere μμ 0 = 4πx10-7T. Unit of Magnetic Flux. Solenoids can be used to electrically open doors and latches, open or close valves, move and operate robotic limbs and mechanisms, and. The unit was named in honor of German scientist Max Weber. Question: Calculate the energy associated with the magnetic field of a 222-turn solenoid in which a current of 1. Magnetic field produced by solenoid is constant inside the solenoid and parallel to the axis of it. Problems An emf of 0. If there is a solenoid of length L , radius R, number of turns N immersed in uniform magnetic field B with axis of the solenoid being parallel to the field, then what will be the flux linkage and the. When a current passes through it, it creates a nearly uniform magnetic field inside. 5Rotation of a coil in a magnetic field produces an emf. Demo: Coil connected to AC source Light bulb connected to second coil (same as solenoid) Demo: Jumping aluminum ring from core of solenoid powered by an AC source. In a solenoid, the core material is ferromagnetic, meaning that it concentrates magnetic lines of flux. Calculate: A. Experimentally, the magnetic flux in a solenoid was measured for various currents I. Griffiths problem 5. Magnetic flux (symbol Φ, 'phi') has the weber (Wb) as its unit and is a measure of the total quantity of magnetic flux. This can be as a result of current carrying conductor produces its own flux. For this project, I cut some small shapes out of 7 mil steel shim material to use as the core. PHY2049: Chapter 30 21 Induced currents ÎA circular loop in the plane of the paper lies in a 3. So our total magnetic field at the center of the circular loop and distance R from the long, straight wire, is the sum of these, 30. Therefore, the variable magnetic field requirement for Faraday’s law is met. The magnetic field strength for a solenoid is given by B=μI*n/l. Thus, the magnetic flux through a circular path whose radius r is greater than R, the solenoid radius, is The induced field is tangent to this path, and because of the cylindrical symmetry of the system, its magnitude is constant on the path. Express the answer in terms of the current through the coil /, the number of turns N, lengthof the coil d. The solenoid force when the solenoid armature starts to close is much lighter than the solenoid force of a working solenoid. across a solenoid when the windings of the solenoid are cut by magnetic flux. If the flux changes: indicate whether it is increasing or decreasing (and in which direction). According to Ohm's law for magnetic circuit, if the field current is invariable, the magnetic flux is in inverse proportion to the magnetic resistance. We have described a solenoid that operates with reduced power and voltage losses and is thus capable to generate uniform magnetic flux density within a significant volume in the coil at high power. The constant u r is essentially unity (= 1. The magnetic field strength for a solenoid is given by B=μI*n/l. A solenoid is a long wire wound around in the form of a helix. It is the flow of magnetism from the north to the south pole of a magnet. The solenoid carries a current of 3 A. The flux through the core links the windings to each other. Longitudinal magnetization of a component can be accomplished using the longitudinal field set up by a coil or solenoid. 4 cm and 400 turns. 78 \times 10^{-4} {/eq} T{eq}\cdot {/eq}m{eq. If the magnetic flux is enhanced by bending the wire into the shape of a coil, and/or wrapping that coil around a material of high permeability, this effect of self-induced voltage will be. (b) The loop is parallel to the field; therefore, η= 90° and Φ= 0. Electric current can be generated suing a solenoid. then the radius of the solenoid r = 1. The top coil's magnetic field is created when it is energized and the same magnetic flux induces the same magneto-motive forces on the plunger (Fig. The maximum current is 10 and the period of the cycle I is T. 0 cm inside the solenoid with its axis coinciding with the axis of the solenoid. - If B is uniform: ΦB = B⊥ A = BA cos ϕ ΦB = ∫B⋅dA = 0 Units : 1 Weber (1 Wb = 1 T m 2 = 1 N m / A) - Difference with respect to electric flux the total magnetic flux through a closed surface is always zero. A)For this time, calculate the average magnetic flux through each turn of the inner solenoid. The magnetic field inside a 25 cm diameter solenoid is increasing at 2. Flaws that run normal to the magnetic lines of flux will disturb the flux lines and often cause a leakage field at the surface of the component. The magnetic flux through circular disks Φ=∫BdA is related to the circulation of the electric field on the circumference ∫Eds. Magnetic Flux Magnetic flux is the quantity of magnetic force lines and is analogous to current in an electric circuit. When a current of 2 ampere is passed through it , the resulting magnetic flux linked with each turn of the solenoid is 4 x 10-3 Wb. Both laws can be used to calculate the net magnetic field produced at a point by various distributions of current. current flow. Usually given the symbol B. 4 A coil wrapped around a solenoid Solutions: (a) The magnetic flux through each turn of the outer coil due to the. The shape of the magnetic flux lines. It should now be clear that the value of v L must be only the tiniest bit less than v G. Thanks for contributing an answer to Electrical Engineering Stack Exchange!. Solenoids can convert electric current to mechanical action, and so are very commonly used as switches. Outside the solenoid, the magnetic field is far weaker. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Magnetic Flux Density, B "Magnetic flux density, B, is the force, F, per unit length, l, per unit current, I, on a current carrying conductor at right angles to the magnetic field. The magnetic flux through a 100-turn coil is increased at a rate of 0. 1 Simple structure of solenoid actuator. Magnetic Field Strength refers to one of two ways that the expression of a magnetic field can take place. The magnetic flux density is also called "B field" or "magnetic induction". 140 \, m} = 2. N of a wire in shape of a helix. Express the answer in terms of the current through the coil /, the number of turns N, lengthof the coil d. 1) has been developed that compares these key values. The atomic moments add up to produce a total magnetic moment for the permanent magnet, and the magnetization M is the total magnetic moment per unit volume. If a loop of wire with an area A is in a magnetic field B, the magnetic flux is given by:. and the relative permeability of the core is k = , then the magnetic field at the center of the solenoid is. The magnet is held stationary to the solenoid. 5 m long and 1. the core creates sturdy magnet. Use of magnetic material for. Solenoid Actuator Design for Improvement of Response Speed 325 Fig. Magnetic Flux Density, B "Magnetic flux density, B, is the force, F, per unit length, l, per unit current, I, on a current carrying conductor at right angles to the magnetic field. In addition, supplemental magnetic flux fields are created in the magnetic circuit paths as a result of the application of the energizing signal to the coil. There is no change in flux when it tilts so the answer is the same: 0. Examples of objects that have magnetic moments include: loops of electric current (such as electromagnets), permanent magnets, moving elementary particles (such as electrons), various molecules, and many astronomical objects (such as many planets, some moons, stars, etc). -cm-diameter solenoid passing through the center of a 5. Therefore, the magnetic flux through the coil is the product of the solenoid’s magnetic field times the area of the coil. Part A Consider first the generation of the magnetic field by the current in solenoid 1. The SI unit of magnetic flux is the weber (Wb; in derived units, volt-seconds), and the CGS unit is the maxwell. Predict/Calculate A solenoid with 385 turns per meter and a diameter of 17. The magnetic flux density B is described by the equation : where μ o is the permeability of free space and n is the number of turns per unit length of the solenoid. Magnetic flux quantum is the quantum of magnetic flux passing through a superconductor. It is likely that soft iron and a permanent magnet have magnetic permeabilities of the same order of magnitude (I haven't checked), so using either as a core could yield a similar current-induced magnetic flux magnitude within the core. 4 A coil wrapped around a solenoid Solutions: (a) The magnetic flux through each turn of the outer coil due to the. where $$V = Al$$ is the volume of the solenoid. Magnetic flux may be thought of as the amount of magnetic field passing through an area. , perpendicular to the plane of each turn. The value of magnetic flux is a vector quantity and it depends. - If B is uniform: ΦB = B⊥ A = BA cos ϕ ΦB = ∫B⋅dA = 0 Units : 1 Weber (1 Wb = 1 T m 2 = 1 N m / A) - Difference with respect to electric flux the total magnetic flux through a closed surface is always zero. The magnetic flux through the solenoid assuming the magnetic field is uniform. The solenoid force when the solenoid armature starts to close is much lighter than the solenoid force of a working solenoid. Kobelev Abstract. 49 A produces a magnetic flux of {eq}3. 3*10^-5 i need help with What is the magnetic flux through the loop when it is tilted at a 60∘ angle?. 5 cm long and wound with 104 turns of wire. 3-9 practically satisfies that condition. 35 s, the magnitude of the induced emf is 0. In the diagram below A, B, C, and D are points in the magnetic field near a current carrying loop. A magnetic flux concentrator is a piece of ferrous material, such as steel, that is used to direct or intensify magnetic flux towards a sensing element. 5 A solenoid of length 25 cm is made using 100 turns of wire wrapped round an iron core. 0 $\mathrm{cm}$ has a magnetic flux through its core of magnitude 1. When energized, a magnetic field builds up which pulls a plunger or pivoted armature against the action of a spring. The Magnetic Field at the Center of a Solenoid (part I) - Duration: 9:58. Magnetic flux is usually measured with a fluxmeter, which. Just like electric current, it is easier for magnetic flux to flow through some materials than others, soft iron for example has. Magnetic Flux. Magnetic Flux Lab. This site has been useful for me. 0 cm 2 = 2 × 10-4 m 2. Purpose: In this activity you will be looking at the circumstances under which a current will flow in a coil of wires. Determine the variables in the situation for which you are trying to calculate the force exerted by the magnetic solenoid. In electromagnetism theory, it is absolutely clear that these are different quantities and you need to be precise about which you are measuring. ∴ θ= 0, so for N turns, Φ= NBA. The permanent magnet generates a small magnetic flux in the magnetic circuit generating an attraction of the armature and the fixed pole piece with no power applied. 0-cm-diameter loop. The best fit line through the data is also drawn. The magnetic flux through one turn is Φ =! B •! A =! B ! A cosθ, but in a solenoid, the flux lines are parallel to the axis of the solenoid, i. The Purpose of the Magnetic Core The fundamental purpose of any magnetic core is to provide an easy path for flux in order to facilitate flux linkage, or coupling, between two or more mag-. If the current through a solenoid increases, the magnetic field strength of the solenoid (1) decreases (3) remains the same (2) increases 33. 30 A, what is the magnetic flux through the square loop? T m2 (b) If the current in the solenoid is reduced to zero in 2. Now, as everybody knows,. Magnetic flux during the valve opening is shown in fig. Magnetic flux due to a solenoid When an electric current is passed through a solenoid or long cylindrical coil the resultant magnetic flux is very similar to that of a bar magnet. ∴ θ= 0, so for N turns, Φ= NBA. The best fit line through the data is also drawn. The magnetic field on the axis at the center of the solenoid. There are 200 turns of wire. The diagram below represents lines of magnetic flux within a region of space. The magnetic flux through this circle (i. A current of 2. Problem 47. (a) Calculate the mutual inductance M, assuming that all the flux from the solenoid passes through the outer coil. The magnetic field inside a 25 cm diameter solenoid is increasing at 2. The strength of the magnetic field (or amount of flux measured in Webers) in a transformer core is directly proportional to the number of TURNS around the coil that is producing the magnetic flux within the core, and to the amount of CURRENT flowing in the coil. Becuase the flux decreases, I keep my right thumb pointing in the direction of the magnetic field, curl my fingers, and find the current in the coil is the other way -- clockwise as viewed from. 0-cm-diameter loop. This increases the inductance of the coil far beyond the inductance obtainable with an air-core coil of the same dimensions and the same number of turns. 00 x 10 - 4 T at its center produced by a current of 1. The magnetic field inside the solenoid is 0. Question: Calculate the energy associated with the magnetic field of a 222-turn solenoid in which a current of 1. The magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. The magnetic flux through a loop might change for a variety of reasons, but in this experiment we will only be concerned with the effect of a sinusoidally varying current in a nearby circuit. Nφ is defined as the flux linkage between each of the coils. How many turns should a coil wrapped around the outside of the solenoid have so that the emf induced in the coil is 15. Metric (SI) Dimensions: length 2 × mass × time-2 × electric-current-1. The magnetic field inside the solenoid is uniform. and the relative permeability of the core is k = , then the magnetic field at the center of the solenoid is. In order to determine the strength of a magnetic field , some useful mathematical equations can be applied. 78 \times 10^{-4} {/eq} T{eq}\cdot {/eq}m{eq. We find the magnetic field produced by solenoid with the following formula; Where: i is the current, N is the number of loops and l. 0 T magnetic field pointing into the paper. Strength of the field diminishes with distance from the solenoid. In more practical terms, Permeability is a measure of a material's ability to absorb magnetic flux. The average magnetic flux through each turn of the inner solenoid. causes alignment of the domains in the iron. Evaluate the number of turns of the solenoid from Faraday's law of electromagnetic induction, which states that the size of electromotive voltage induced in the solenoid is proportional to the change in magnetic flux through the solenoid per given time. Some magnetic flux appears outside the coil (near ends of the core) and a small amount of flux flows off across the coil. The magnetic flux inside a solenoid is uniform. Calculate themagnetic flux linkage for this solenoid. Thus any other material kept around the solenoid through which the electric current is passing experiences magnetism. Solenoid - Magnetic field, Magnetic Flux, Self Inductance Solenoid is a coil of large number of loops made of conducting wire. The magnetizing force, which induces the lines of force through a material, is. 00 cm, as shown in the end view of the figure below. Examples of objects that have magnetic moments include: loops of electric current (such as electromagnets), permanent magnets, moving elementary particles (such as electrons), various molecules, and many astronomical objects (such as many planets, some moons, stars, etc). Abstract: Magnetic flux leakage (MFL) testing is a widely applied method for the ferromagnetic specimen defect detection. A possible solution was introduced using magnetic flux tailoring Lenz lenses, which were recognized recently to locally amplify the magnetic field at a given region of interest by Schoenmaker et al. It is the flow of magnetism from the north to the south pole of a magnet. The motion of a charged particle in homogeneous perpendicular electric and magnetic fields (L4) Magnetic flux through a square (L4) Varying Magnetic Flux trough Solenoid (L2) Conductor Moving in a Magnetic Field (L2) Voltage Induced in a Rotating Circular Loop (L3) A single loop receding from a wire (L3) Inductance of a Coil (L2) Inductance of. Examples of objects that have magnetic moments include: loops of electric current (such as electromagnets), permanent magnets, moving elementary particles (such as electrons), various molecules, and many astronomical objects (such as many planets, some moons, stars, etc). Chapter 32 Inductance and Magnetic Materials The appearance of an induced emf in a circuit associated with changes in its own magnet field is called self-induction. Magnetic flux due to a solenoid When an electric current is passed through a solenoid or long cylindrical coil the resultant magnetic flux is very similar to that of a bar magnet. In more practical terms, Permeability is a measure of a material's ability to absorb magnetic flux. Around the bar magnet, the flux is greatest around the poles. Each of the smaller solenoids would induce current. The magnetic field on the axis at the center of the solenoid. This will produce a sinusoidally varying magnetic field, which causes a flux of magnitude ! B(t) =(Bsin"t)NAcos# (3) The voltage induced is given by. Electric current can be generated suing a solenoid. In a solenoid of N loops and uniform magnetic field B, the magnetic flux is B*N*A, where A represents the area surrounded by each loop. Calculate: A. The Earth’s magnetic field resembles that of a large bar magnet titled at about 10 ° to Earth. (b) Find the magnetic flux through the coil if R2 < R1. Thus, This result is the same as the one for the infinite solenoid. Are you asking for the equation or a qualitative description? Ampere observed that a magnetic field is generated around an electrical current. A well known. Abstract: Magnetic flux leakage (MFL) testing is a widely applied method for the ferromagnetic specimen defect detection. In general, one determines Φ \Phi Φ as a function of t t t, which allows for the. When current is passing through an ideal solenoid, a magnetic field is created in which the lines are horizontal passing straight through the solenoid. the magnetic filed B = 0. How many turns should a coil wrapped around the outside of the solenoid have so that the emf induced in the coil is 15. The soft-magnetic stainless steel part of the solenoid which is moved by magnetic forces (flux generated by the coil). Outside the solenoid, the magnetic field is zero. Magnetic Induction 2665 6 • Give the direction of the induced current in the circuit, shown on the right in Figure 28- 37, when the resistance in the circuit on the left is suddenly (a) increased and (b) decreased. We define magnetic flux as the total number of magnetic lines of force in a magnetic field. Some magnetic flux appears outside the coil (near ends of the core) and a small amount of flux flows off across the coil. Procedure. The magnetic flux through the solenoid assuming the magnetic field is uniform. The data was recorded in the table below, and plotted in the graph on the right. External flux concentrators have long been used externally to direct and concentrate magnetic flux in Hall-effect applications. Permanent magnet always creates the magnetic flux and it does not vary upon the other external factors. The expression of the magnetic field is given by. The strength of this field depends on the current, the number of windings and the material of the core. (i) When the distance between a pair of coils is increased, the magnetic flux linked with the secondary coil decreases and hence, the mutual inductance between them will decrease. The term solenoid was coined in 1823 by André-Marie Ampère to designate a helical coil. 20T (a) flux=(magnetic field)(area)(costheta) The magnetic flux through the loop: φ = BAcosθ = Bπr^2 cos90 = (0. The magnetic field inside a 25 cm diameter solenoid is increasing at 2. Results and Discussion 3. Inductors and Inductance - Duration: 8:36. Info: The program you will be using to complete this lab can be activated by clicking here. Explain your answer. Magnetic Flux Magnetic flux is the quantity of magnetic force lines and is analogous to current in an electric circuit. Magnetic flux density (B) is the amount of magnetic flux concentrated in a given cross-sectional area and has the units of webers per square. The magnetic field inside the solenoid is uniform. Magnetic flux linkage ʌ is total magnetic liking flux in a circuit. In addition, these magnetic lines form closed loops that leave at the north pole of the magnet and enter at the south pole. (a) Find the current in this solenoid. 5 m long and 1. 2 m in diameter is 1. If there is a solenoid of length L , radius R, number of turns N immersed in uniform magnetic field B with axis of the solenoid being parallel to the field, then what will be the flux linkage and the. In the most general form, magnetic flux is defined as φB = ∬AB ⋅ dA. Inductance and magnetic B-field. Magnetic flux is the quantity of magnetic field that penetrates an area at right angles to it. Core form of solenoid: A solenoid is a basic device, which is used to provide an electromagnetic path in order to transmit maximum magnetic flux density with minimum input of energy. 30 A, what is the magnetic flux through the square loop? T m2 (b) If the current in the solenoid is reduced to zero in 2. The Solenoid. The unit of magnetic flux density is called the Tesla. Flux is obtained by integrating the flux density over the surface area. 0*10^-2m)^2 = 0. 2A flowing, calculate the flux density and total flux. 3-9 practically satisfies that condition. The magnetic flux through the solenoid assuming the magnetic field is uniform. Experiment with the sliders and note how H and B are related to each other and the. Write the change in the magnetic flux through this circle in 2. 121P11-33 increases according to the relation ΦΦΦΦ B = 6. Express the answer in terms of the current through the coil /, the number of turns N, lengthof the coil d. Magnetic field produced by solenoid is constant inside the solenoid and parallel to the axis of it. Magnetic flux is the rate of change of magnetic field. All of the magnetic flux is forced to flow through this area. When current flows through the coil, a magnetic field is created around the coil. The magnetic flux through this circle (i. As shown above, the magnetic field is strongest near to the poles of the magnet were the lines of flux are more closely spaced. A For the solenoid above, the. A solenoid consists of many turns N of a wire in shape of a helix. Additionally to the present, the core behaves sort of a magnet due to magnetic induction, producing its own flux. If the average diameter of the solenoid is 3 cm and it carries a current of 4 A, find the magnetic field at a point well within the solenoid. Therefore, the energy density (energy per unit volume) is given. 30 A, what is the magnetic flux through the square loop? T m2 (b) If the current in the solenoid is reduced to zero in 2. The goal of this lab exercise is to “discover” the properties of the magnetic field of a solenoid. 00 cm, as shown in the end view of the figure below. The expression of the magnetic field is given by. We assume that the solenoid is long enough such that there is not field outside the solenoid, and therefore the flux through the cross section of the solenoid is the flux through the. 49 A produces a magnetic flux of {eq}3. (a) The loop is perpendicular to the field; hence, η= 0, and Φ= BA. (a) Find the magnetic flux through the coil if R2 > R1. The solenoid force when the solenoid armature starts to close is much lighter than the solenoid force of a working solenoid. If we place an imaginary isolated unit north pole in a magnetic field it will experience a repulsive force from north pole and an attractive force from south pole of the magnet which has created the field. Start studying Physics Exam 2 Concept Questions. Optimal Bitter Coil Solenoid 1 Optimal Bitter Coil Solenoid V. CiteSeerX - Document Details (Isaac Councill, Lee Giles, Pradeep Teregowda): In some textbooks on quantum mechanics, the description of flux quantization in a superconductor ring based on the Aharonov-Bohm effect may lead some readers to a (wrong) conclusion that flux quantization occurs as well for a long solenoid with the same quantization condition in which the charge of cooper pair 2e is. The solenoid has a small loop of area, A =2. The book is saying that the flux through the solenoid is B(pi)(R^2) not BN(pi)(R^2). Resistive Paper. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. 8-cm-diameter loop. Write the change in the magnetic flux through this circle in 2. For an ideal solenoid, there is a constant magnetic field. Core form of solenoid: A solenoid is a basic device, which is used to provide an electromagnetic path in order to transmit maximum magnetic flux density with minimum input of energy. The unit was named in honor of German scientist Max Weber. Electromagnetism index. Determine the variables in the situation for which you are trying to calculate the force exerted by the magnetic solenoid. Properties of Magnetic Flux. Magnetic Flux Density, B "Magnetic flux density, B, is the force, F, per unit length, l, per unit current, I, on a current carrying conductor at right angles to the magnetic field. As mentioned in the description of both magnetic network models, one can tell the higher armature flux and inductance of the advanced solenoid model at large air gaps compared to that of the simple model. External flux concentrators have long been used externally to direct and concentrate magnetic flux in Hall-effect applications. This is called a uniform field. Some magnetic flux appears outside the coil (near ends of the core) and a small amount of flux flows off across the coil. Magnetic flux; In context. magnetic flux leakage (MFL) device for the evaluation of hidden prestressing strand under the surface of prestressed concrete box beams was designed, developed, and tested in the laboratory. Investigation of magnetic flux density using a Hall probe. where B is the magnetic flux density, l is the length of the solenoid, μ 0 is the magnetic constant or the magnetic permeability in a vacuum, N is the number of turns in the coil, and I is the current through the coil. m/A 0 4x 10T. Magnetic Flux and Gauss's Law for Magnetism ΦB = ∫B⊥dA = ∫B ⋅dA = ∫B⋅dA cos ϕ - Magnetic flux is a scalar quantity. You must understand how induced electric fields give rise to circulating currents called “eddy currents. Solenoids and Magnetic Fields This lecture is based on HRW, Section 30. Using this formula and the Rowland’s Law formula, calculate the amount of magnetic flux (Φ) produced in the throat of an air-core solenoid with 250 turns of wire, a length of 0. This is a derivation of the magnetic flux density around a solenoid that is long enough so that fringe effects can be ignored. These are also called magnetic flux lines. The book is saying that the flux through the solenoid is B(pi)(R^2) not BN(pi)(R^2). For a tightly wrapped solenoid, the flux linkage is the number of loops multiplied by the total flux linking them. 0 t, where ΦΦΦΦ B is in milliwebers and t is in seconds. 4 A coil wrapped around a solenoid Solutions: (a) The magnetic flux through each turn of the outer coil due to the. Among these components solenoid plunger is the final actuating component, when the solenoid coil has been electrified, the magnetic field is created, and the solenoid iron core is magnetized so that the plunger can move to trigger the device. \] The magnetic field produced inside the solenoid is. Problem 47. A well known. Core form of solenoid: A solenoid is a basic device, which is used to provide an electromagnetic path in order to transmit maximum magnetic flux density with minimum input of energy. The unit of magnetic flux density is called the Tesla. The average magnetic flux through each turn of the inner solenoid. In other words, the magnetic flux is maximum when. 1) clockwise 2) counterclockwise 3) no induced current. Some magnetic flux appears outside the coil (near ends of the core) and a small amount of flux flows off across the coil. The high stresses due to Lorentz forces in the coil is one principal constraint. The magnetic field within a solenoid depends upon the current and density of turns. Magnetic Flux. A solenoid is a coil of wire designed to create a strong magnetic field inside the coil. Browse other questions tagged solenoid magnetic-flux or ask your own question. Optimal Bitter Coil Solenoid 1 Optimal Bitter Coil Solenoid V. The magnetic flux through a 100-turn coil is increased at a rate of 0. The dimension of this electro-magnet is responsible to create the strength the magnetic field and. 0 henry (c) 2. The changing current in the solenoid produces a changing flux in the loop. In Figure 1, we immediately know that the flux density vector points in the positive z direction inside the solenoid, and in the negative z direction outside the solenoid. Ignoring end effects, the total magnetic flux through the coil is obtained by multiplying the flux density by the cross-section area : =. The magnetic flux is always defined with respect to a given area. Terms used in electromagnetism. 6 cm, a radius equal to 0. Electromagnetic machines inevitably contain iron or another ferromagnetic material. 0 $\mathrm{cm}$ has a magnetic flux through its core of magnitude 1. A solenoid that has a length equal to 24. If there is a solenoid of length L , radius R, number of turns N immersed in uniform magnetic field B with axis of the solenoid being parallel to the field, then what will be the flux linkage and the. The magnetic field is expressed as the product of the magnetic strength and the direction of the moving charges. Core form of solenoid: A solenoid is a basic device, which is used to provide an electromagnetic path in order to transmit maximum magnetic flux density with minimum input of energy. Some magnetic flux appears outside the coil (near ends of the core) and a small amount of flux flows off across the coil. Determine the magnetic flux density at a point on the axis of a solenoid with radius b and length L, and with a current I in its N turns of closely wound coil. The magnetic field produced by an MRI solenoid 2. Both magnetic fields store some energy. More loops will bring about a stronger magnetic field. Magnetic Field of a Solenoid. When a magnet is moved in or out of the coil, current flows in the coil. Picture the Problem The magnetic field outside the solenoid is, to a good approximation, zero. 00 cm, and (c) L = 12. Covered concepts: Magnetic field, magnetic flux, magnetic force, induced current, solenoids and loops, Lenz’s law, power, RL circuit Chapter 23: Magnetic Flux and Faraday’s Law of Induction. 3): A graph of the magnetic flux density (B) against the magnetising force (H) is called the magnetising curve. 30 m) has a magnetic field of 4. During the solenoid armature pull-in process, the magnetic flux grows larger, which means the attractive force of dc solenoid is related to the position of the solenoid armature. Now consider a circle of radius r (less than a) perpendicular to the axis of the solenoid (and hence to the field B). Magnetic flux density conversion calculator converts tesla, Gauss, weber per meter square, line per square inch, gamma vice versa with metric conversion. Magnetic flux is the quantity of magnetic field that penetrates an area at right angles to it. Core Spring Spring which returns the core to the original position when the coil is de-energized. of turns per unit length. Longitudinal magnetization of a component can be accomplished using the longitudinal field set up by a coil or solenoid. 4 cm and 400 turns. The expression of the magnetic field is given by. For example, if the coil bobbin width is 30mm, a. 75 s, what is the magnitude of the average induced emf in the square loop?. 4 FARADAY’S LAW OF INDUCTION From the experimental observations, Faraday arrived at a conclusion that an emf is induced in a coil when magnetic flux through the coil changes with time. Additionally to the present, the core behaves sort of a magnet due to magnetic induction. Core Tube Stainless steel tube, closed at one end, which isolates the media in the valve from the external solenoid parts. 5 s What is the magnitude of the average induced emf? What is the direction of the induced current? If the coil resistance is 0. solenoid magnet - turns,volts,amps. Flaws that run normal to the magnetic lines of flux will disturb the flux lines and often cause a leakage field at the surface of the component. A current of 2. The magnetic field generated in the centre, or core, of a current carrying solenoid is essentially uniform, and is directed along the axis of the solenoid. causes alignment of the domains in the iron. The electromagnetic force on the plunger is the gradient of the accumulated energy in the working air gap and core of the solenoid. Magnetic flux quantum is the quantum of magnetic flux passing through a superconductor. Core form of solenoid: A solenoid is a basic device, which is used to provide an electromagnetic path in order to transmit maximum magnetic flux density with minimum input of energy. Any change in flux must be produced by a change in the current, D I, since m 0, n, and A remain constant. The magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. 0 cm long and has a diameter of 2. If we place an imaginary isolated unit north pole in a magnetic field it will experience a repulsive force from north pole and an attractive force from south pole of the magnet which has created the field. Such coils, called solenoids, have an enormous number of practical applications. (a) If the current in the solenoid is 2. 008 m The magnetic flux through an annulus shaped solenoid -rl -(0 004m)2) Step 3 of 5. (a) Consider a circle of radius 1. 1), what is the magnitude of I. Solenoid: A solenoid produces a magnetic field similar to that of a permanent bar magnet. Several magnetic flux gauges will be attached to the. Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. 58 x 10-5 Wb. The solenoid is 24. The magnetic field inside the solenoid is directly proportional to the current flowing in the solenoid and the no. Magnetic field and magnetic flux both refer to properties of magnets. In the presence of a magnetic field, magnetic flux Φ exists. A 'hand-waving' explanation might help clarify the physics. The Right-Hand Rules give only the direction of the magnetic field. According to the right-hand rule, an induced clockwise current will generate a magnetic field into the page. D) Halving the radius of the coil halves the magnetic flux through the coil. The magnetic field on the axis at the center of the solenoid. Longitudinal magnetization of a component can be accomplished using the longitudinal field set up by a coil or solenoid. Solenoids and Magnetic Fields This lecture is based on HRW, Section 30. % Magnetic Flux distribution using Finite Element Method % of a Solenoid Vertically placed on XY plane. Core Tube Stainless steel tube, closed at one end, which isolates the media in the valve from the external solenoid parts. 05Ω, what is the average induced current?. As a result of the magnetic field, the solenoid core is pulled towards the centre of the coil. A solenoid is in an upright position on a table. The Magnetic Field at the Center of a Solenoid (part I) - Duration: 9:58. a loop in a magnetic field that is decreasing c. The SI unit of magnetic flux is the weber (Wb): 1 Wb =1 T⋅m2 Faraday's law of induction may be stated as follows: The induced emf ε in a coil is proportional to the negative of the rate of change of magnetic flux: B d dt ε Φ =− (10. (b) at the centre of a solenoid of 2000 turns 75 cm long when a current of 1. 0 A creates a magnetic field of flux density 2 × 1 0 − 5 2\times10^{-5} 2 × 1 0 − 5 T through the core of this solenoid. Note 6: The calculated magnetic at a distance from the center of the coil, see Figure 2. flux: The rate of transfer of energy (or another physical quantity) through a given surface, specifically electric flux or magnetic flux. On the other hand, magnetic flux is the measure of the magnetic field strength of a two dimensional surface, say one particular side of a magnet. Air gap, also airgap 1) or air-gap 2) - is a non-magnetic part of a magnetic circuit. causes alignment of the domains in the iron. The Magnetic Field of a Solenoid Magnetic Flux and Gauss's Law Faraday's Law of Induction. According to Ohm's law for magnetic circuit, if the field current is invariable, the magnetic flux is in inverse proportion to the magnetic resistance. Predict/Calculate A solenoid with 385 turns per meter and a diameter of 17. When current is caused to flow within a solenoid, a magnetic field will appear around and inside the form, looking like the magnetic field around a bar magnet. 1), what is the magnitude of I. The changing current in the solenoid produces a changing flux in the loop. magnetic field lines electric field lines dt d Eds B C!#=" rr The electric current produces a magnetic field B=µ 0 ni, which changes with time, and produces an electric field. A magnetic field with magnitude B = 1 T is a strong field. Magnetic flux is the quantity of magnetic field that penetrates an area at right angles to it. This increases the inductance of the coil far beyond the inductance obtainable with an air-core coil of the same dimensions and the same number of turns. Note: The magnetic field pattern outside the solenoid is just the same as a bar magnet, with a north and south pole and the magnetic flux lines flowing from north to south. The expression of the magnetic field is given by. 1 [Wb] = 108 [Mx]. Calculate the magnetic field: ( )( ). How is the magnetic flux through the solenoid affected by changing the magnetic field strength?. 49 A produces a magnetic flux of {eq}3. \$ (a) Find the current in this solenoid. Magnetic Field around a Solenoid Picture given below shows the solenoid. The unit of magnetic induction is the tesla (T). where Φ \Phi Φ is the magnetic flux through the loop (recall that emf points in the opposite direction as the voltage). As mentioned in the description of both magnetic network models, one can tell the higher armature flux and inductance of the advanced solenoid model at large air gaps compared to that of the simple model. The Magnetic Field of a Solenoid Magnetic Flux and Gauss's Law Faraday's Law of Induction. 4 cm and 400 turns. Both laws can be used to calculate the net magnetic field produced at a point by various distributions of current. 20T (a) flux=(magnetic field)(area)(costheta) The magnetic flux through the loop: φ = BAcosθ = Bπr^2 cos90 = (0. The magnetic flux over some area A is defined as (1) Φ=∫ ⋅ KK Bda A In the case that the B-field is uniform and perpendicular to the area , (1) reduces to (2) Φ=B⋅A. In the study of electromagnetism, a solenoid is a coil whose length is substantially greater than its diameter. Express the answer in terms of the current through the coil /, the number of turns N, lengthof the coil d. The magnetic field inside a 25 cm diameter solenoid is increasing at 2. Due to change in the magnetic flux linked with the coil, an e. Now, as everybody knows,. However, in magnetic circuits where there is magnetic leakage and the flux follows paths such that different amounts of flux link different numbers of turns in the exciting winding, the value of Φ in Eqs. A special matrix (Fig. When current is passing through an ideal solenoid, a magnetic field is created in which the lines are horizontal passing straight through the solenoid. The material begins to lose its magnetic properties. 2? We can build the solenoid with the larger cross-sectional area, 2*A, out of two solenoids with the initial cross-sectional area, A. Think about How does the field vary along the axis? Solenoid. the cross-sectional area of the solenoid, c. Symbol B The amount of magnetic flux through a unit area taken perpendicular to the direction of the magnetic flux. The solenoid carries a current of 3 A. Each of the smaller solenoids would induce current. Field lines outside the solenoid are similar to that of a bar magnet, and it behaves in a similar way – as if it had a north pole at one end and south pole at the other end. Examples of objects that have magnetic moments include: loops of electric current (such as electromagnets), permanent magnets, moving elementary particles (such as electrons), various molecules, and many astronomical objects (such as many planets, some moons, stars, etc). Magnetic Induction 2665 6 • Give the direction of the induced current in the circuit, shown on the right in Figure 28- 37, when the resistance in the circuit on the left is suddenly (a) increased and (b) decreased. Any change in flux must be produced by a change in the current, D I, since m 0, n, and A remain constant. In what sequence of a rectangular loop will the magnetic flux through the loop decrease? A permanent bar magnet with the south pole pointing downward is dropped through a solenoid, what is the. This can be as a result of current carrying conductor produces its own flux. Note: L is inductance and l (italicized lowercase L) is length. 66370614 nano webers. 4 cm and 400 turns. Induced emf is the rate of change magnetic flux. Introduction. Both laws can be used to calculate the net magnetic field produced at a point by various distributions of current. In the study of electromagnetism, a solenoid is a coil whose length is substantially greater than its diameter. The term solenoid was coined in 1823 by André-Marie Ampère to designate a helical coil. 30 A, what is the magnetic flux through the square loop? T m2 (b) If the current in the solenoid is reduced to zero in 2. The magnetic flux through circular disks Φ=∫BdA is related to the circulation of the electric field on the circumference ∫Eds. conductor motion. But electromagnet creates its variable magnetic fields based on how much current it carries. N of a wire in shape of a helix. The inductance of a solenoid is close to L=μr²n²π/l, but diverges increasingly from this estimation as the length becomes shorter relative to the radius. 45966*10^-8. However, there is zero magnetic field outside the solenoid. \] The magnetic field produced inside the solenoid is. The developed electromagnetic force depends on the solenoid current and the inductance gradient[2]. A solenoid. (a) Consider a circle of radius 1. 3) For a coil that consists of N loops, the total induced emf would be N times as large: B d N dt ε Φ. This design is a significant improvement over simple solenoids that often have significant field inhomogeneity and losses. Whereas, the magnetic flux shows the quantities of the magnetic lines of force passes through it. 4 A coil wrapped around a solenoid Solutions: (a) The magnetic flux through each turn of the outer coil due to the. If the same solenoid was wound around a wrought iron core with μ r = 500 and a current 0. The changing current in the solenoid produces a changing flux in the loop. The unit of magnetic flux in the Weber (Wb). The solenoid force when the solenoid armature starts to close is much lighter than the solenoid force of a working solenoid. Flux is obtained by integrating the flux density over the surface area. Magnetic flux is represented by the symbol , therefore we can say that = BAcos(a) and the resulting unit will be , where T is the unit for magnetic field and is the unit for area. Solenoid A solenoid is a coil wound in a helical manner, which can be used to generate a nearly uniform magnetic field similar to that of a bar magnet, when an electric current is passed through it [8]. Flux Density inside a Long Coil (Solenoid) Current flowing through a conductor produces a magnetic field. If the north pole of the magnet is moved towards the coil, the magnetic flux through the coil increases as shown in above figure.


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# Would there still be land if the amount of water in the oceans was doubled?

A portal to another Earth in a parallel universe is open at the bottom of the Ocean and all the water is moving to the new Earth in the form of a waterfall in the middle of the Atlantic. The form of new Earth is exactly like ours.

• Is there still land available? If yes, how much?

I'm focusing on this new Earth.

• Please specify what do you mean by land, some of them float you know... – user6760 Mar 6 at 10:59
• Floating land is ok. – Malkev Mar 6 at 11:10
• the icecaps would not melt and flow to the other earth. Also there are places in oceans that are deeper that atlantic. this water would also not flow through your bottle. Additionally, a bottle is not very wide, so it would take reasonable time for the water to flow through. I do not know how to calculate that time, but I would assume at leadt several years. That can be very important for a story. – Julian Egner Mar 6 at 11:29
• Randall munroe did some calculations on the speed and possible obstacles what-if.xkcd.com/53 – Borgh Mar 6 at 12:07

The average depth of the ocean is about 3,7 km about a third of the world is not-ocean. So the new average depth would be 3,7 + (3,7*(2/3)) = 6.17 km, or 2,46 km deeper than it is now.

So yes, there would be land. But only where we currently have reasonably high mountains. In Europe for example only the Alps and Pyrenees would remain above water. The only significant land mass left would be the Tibetan plateau I have made a map of Asia assuming water level is 2500m above sea level

• So I need to search for land higher to 2,46 km to obtain our new map? Isn't Ice in the poles affected by the new water? – Malkev Mar 6 at 11:15
• Total sea level rise if all the ice on earth melted would be less than 100 meters. So for the purpose of this question I ignored it. – Borgh Mar 6 at 11:31
• I don't think doubling the amount of water equates to doubling the depth of the ocean. At the very least because $4\pi r^2 dr$ is increasing with $r$. – Alexis Mar 6 at 11:58
• @Alexis, earth is large enough (and the numbers you find so big, for example the volume of earth is 260 billion km3, the water 1,486 billion km3) that in cases like this (adding a few km) you might as well approach it like a flat plane. – Borgh Mar 6 at 13:05
• This is a good map, well made, but did we take into account that the area of the ocean increases as it fills? the larger the surface area the more water it takes to make it rise. It does seem you have done this but i just want to double check – Elias Rowan Albatross Mar 6 at 17:00

Under the assumption that the new earth is exactly like ours, there will be small fraction of land available, when all the water in our earth flows to the new earth.

Just to explain more, lets assume earth's oceans contains around 3.5 kilometers of water. Ocean depth ranges from around few meters to even 10 KM. But for our calculation lets use the number 3.5 KM as average.

If this is doubled, the depth becomes 5.9 ~ 6KM. If our assumptions are right, then we can see these mountain ranges and structures with elevations > 2.5 KM in the new earth.

Edit : Corrected calculations. Thanks @Borgh, @Malkev and @Tim B

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### Dealing with Winter

Guest post by Erin

So many recent conversations with friends near and far have begun with some variation of these phrases: "How's your family dealing with the weather?" or "I bet you're really missing California/Hawaii right now?!?!?"

There's often a subtle look of disappointment when John or I report that it's not too bad.  Yes, there's too much snow and nowhere to put it. Yes, it's getting old that the kids have missed 6 days of school in the last month.  But then again, there's a strange comfort in our current inability to control what's falling from the sky and piling up on our streets and sidewalks.  EVERYWHERE!  And our kids are really helping us to make the best of it. This morning as I marveled at the accumulation, my little contrarian MJ informed me that "Mom, that's not really THAT much snow."

When asked what he thinks about all of the weather, OJ said, "You know, I like that we get all of the seasons.  If I want sunshine, I just wait until summer.  In winter, we get snow and it's so much fun to play in the snow, and we never got to do that in California"

He's on to something there. Living in a place with a clear delineation between seasons adds a pace to life that I've not experienced living elsewhere. Growing up in Houston, TX I knew life with two seasons-- drab, cold winter (wrap the pipes and cover the azaleas) and oppressively hot and humid summer (move from one air-conditioned building to another or to a swimming pool).  Seven years in Northern CA showed me that there are flowers that bloom year round.  And, there's nothing quite like leaving work in sunny Danville and traveling west on Hwy 24 to emerge from the Caldecott Tunnel into a massive wall of fog.  Honolulu, HI is truly a tropical paradise with so many different beaches and seldom a need to wear much more than a bathing suit (especially if you don't have air conditioning!).  In Pasadena, CA, 75-90 degrees and sunny was the lovely, lovely default.

But I'm finding comfort in embracing each season in Cambridge for what it is.  When Spring buds and the temperatures start to approach 65, we shed layers of clothing and laugh when co-eds shed too many to soon to sunbathe by the Charles River. Neighbors gather at the parks just to enjoy being outside, together.  Summer brings trips to swim in Walden pond and dinners cooked entirely on the grill.  I absolutely love running along the Charles river in the Fall when temperatures start to drop and planning Thanksgiving dinner. And then comes winter and snow.

With two active boys and having never lived in a place with snow, I was naturally worried before moving here.  A friend back in SoCal gave the best piece of advice about moving to New England - enjoy each season for what it is and dress accordingly.  She insisted that we invest in waterproof boots, coats and gloves and get outside often to enjoy the snow--- and she was right! Having warm gear has kept us warm enough to build a snow fort and miniature sledding hill in our tiny yard.  We team up with neighbors to keep the sidewalk clear, which involves a system of kids pushing their snow shovels down the sidewalk to an empty yard where we, adults, wait to heave shovels-full over the fence.

Yesterday, in preparation for a week with no school, we borrowed our weight in books from the Cambridge Public Library. Then we headed to Fresh Pond for some proper sledding.  It. Was. Awesome. I loved it as much as the boys did!

A few weeks ago at school-pickup time parents gathered at the entrance to the school and were chatting about preparations for blizzard #2.  One mom shared that she didn't mind snow days because they give us an excuse to just stop.  We can stop rushing, stop worrying about going places and doing things.  I love this mentality and am working hard to embrace it.  It's akin to the practice in yoga of finishing a series of challenging postures with shavasana or "dead-body-pose".  The purpose is to dedicate the same amount of focus and intention you give to a challenging posture to just being still. Our bodies need it to fully receive the benefits of the practice. Our minds and spirits need it too. It helps me to think of winter this way, as a time to rejuvenate. When everything else just waits.

### On the Height of J.J. Barea

Dallas Mavericks point guard J.J. Barea standing between two very tall people (from: Picassa user photoasisphoto).

Congrats to the Dallas Mavericks, who beat the Miami Heat tonight in game six to win the NBA championship.

Okay, with that out of the way, just how tall is the busy-footed Maverick point guard J.J. Barea? He's listed as 6-foot on NBA.com, but no one, not even the sports casters, believes that he can possibly be that tall. He looks like a super-fast Hobbit out there. But could that just be relative scaling, with him standing next to a bunch of extremely tall people? People on Yahoo! Answers think so---I know because I've been Google searching "J.J. Barea Height" for the past 15 minutes.

So I decided to find a photo and settle the issue once and for all.

I then used the basketball as my metric. Wikipedia states that an NBA basketball is 29.5 inches in circumfe…

### Finding Blissful Clarity by Tuning Out

It's been a minute since I've posted here. My last post was back in April, so it has actually been something like 193,000 minutes, but I like how the kids say "it's been a minute," so I'll stick with that.
As I've said before, I use this space to work out the truths in my life. Writing is a valuable way of taking the non-linear jumble of thoughts in my head and linearizing them by putting them down on the page. In short, writing helps me figure things out. However, logical thinking is not the only way of knowing the world. Another way is to recognize, listen to, and trust one's emotions. Yes, emotions are important for figuring things out.
Back in April, when I last posted here, my emotions were largely characterized by fear, sadness, anger, frustration, confusion and despair. I say largely, because this is what I was feeling on large scales; the world outside of my immediate influence. On smaller scales, where my wife, children and friends reside, I…

### The Force is strong with this one...

Last night we were reviewing multiplication tables with Owen. The family fired off doublets of numbers and Owen confidently multiplied away. In the middle of the review Owen stopped and said, "I noticed something. 2 times 2 is 4. If you subtract 1 it's 3. That's equal to taking 2 and adding 1, and then taking 2 and subtracting 1, and multiplying. So 1 times 3 is 2 times 2 minus 1."

I have to admit, that I didn't quite get it at first. I asked him to repeat with another number and he did with six: "6 times 6 is 36. 36 minus 1 is 35. That's the same as 6-1 times 6+1, which is 35."

Ummmmm....wait. Huh? Lemme see...oh. OH! WOW! Owen figured out

x^2 - 1 = (x - 1) (x +1)

So $6 \times 8 = 7 \times 7 - 1 = (7-1) (7+1) = 48$. That's actually pretty handy!

You can see it in the image above. Look at the elements perpendicular to the diagonal. There's 48 bracketing 49, 35 bracketing 36, etc... After a bit more thought we…


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Document Type : Research Paper

Author

Department of Mathematics, Faculty of Basic Sciences, Azarbaijan Shahid Madani University, Tabriz, I. R. Iran.

Abstract

By substituting the usual notion of open sets in a topological space $X$ with a suitable collection of maps from $X$ to a frame $L$, we introduce the notion of L-topological spaces. Then, we proceed to study the classical notions and properties of usual topological spaces to the newly defined mathematical notion. Our emphasis would be concentrated on the well understood classical connectedness, quotient and compactness notions, where we prove the Thychonoff's theorem and connectedness property for ultra product of $L$-compact and $L$-connected topological spaces, respectively.

Keywords

Main Subjects

###### ##### References
[1] A. Bajravani and A. Rastegar, On the Smoothness of Functors, Iranian Journal of Mathematical Sciences and Informatics., 5(2010), pp. 27-39.
[2] E. Bredon Glen, Topology and Geometry, Graduate Texts in Mathematics 139, Springer, 1993.
[3] S. Burris and H.P. Sankappanavar, A Course in Universal Algebra, Springer-Verlag, 1981.
[4] A. Hatcher, Algebraic Topology, Cambridge University Press; 2002.
[5] J.R. Munkres, Topology, Second Edition, Prentice Hall, Inc; 2000.
[6] D.G. Wright, Thychonoff's Theorem, Proceedings of the A. M. S., 120, 1994.


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# Split array into chunks (JavaScript, Python, PHP)

## Problem

Given a list and an integer chunk size, divide the list into sublists, where each sublist is of chunk size.

## Codes

Just for practicing, I've coded to solve the problem using JavaScript and Python. There is also a built-in PHP function for that. If you'd like to review the codes and provide any change/improvement recommendations, please do so and I'd really appreciate that.

### Python

"""
# Problem
# Given a list and chunk size, divide the list into sublists
# where each sublist is of chunk size
# --- Examples: (Input List, Chunk Size)    =>  Output List
# ([1, 2, 3, 4], 2)                 =>  [[ 1, 2], [3, 4]]
# ([1, 2, 3, 4, 5], 2)          => [[ 1, 2], [3, 4], [5]]
# ([1, 2, 3, 4, 5, 6, 7, 8], 3)     => [[ 1, 2, 3], [4, 5, 6], [7, 8]]
# ([1, 2, 3, 4, 5], 4)          => [[ 1, 2, 3, 4], [5]]
# ([1, 2, 3, 4, 5], 10)             => [[ 1, 2, 3, 4, 5]]
"""
from typing import TypeVar, List
import math

T = TypeVar('T')

def chunk_with_slice(input_list: List['T'], chunk_size: int) -> List['T']:
if chunk_size <= 0 or not isinstance(input_list, list):
return False

start_index = 0
end_index = chunk_size
iteration = len(input_list) // chunk_size
chunked_list = input_list[start_index:end_index]
output_list = []
output_list.append(chunked_list)

if (len(input_list) % chunk_size != 0):
iteration += 1
for i in range(1, iteration):
start_index, end_index = end_index, chunk_size * (i + 1)
chunked_list = input_list[start_index:end_index]
output_list.append(chunked_list)

return output_list

def chunk_slice_push(input_list: List['T'], chunk_size: int) -> List['T']:
if chunk_size <= 0 or not isinstance(input_list, list):
return False

output_list = []
start_index = 0

while start_index < len(input_list):
chunked_list = input_list[start_index: int(start_index + chunk_size)]
output_list.append(chunked_list)
start_index += chunk_size
return output_list

if __name__ == '__main__':
# ---------------------------- TEST ---------------------------
DIVIDER_DASH = '-' * 50
GREEN_APPLE = '\U0001F34F'
RED_APPLE = '\U0001F34E'

test_input_lists = [
[10, 2, 3, 40, 5, 6, 7, 88, 9, 10],
[-1, -22, 34],
[-1.3, 2.54, math.pi, 4, '5'],
[math.pi, 2, math.pi, 4, 5, 'foo', 7, 8,
'bar', math.tau, math.inf, 12, math.e]
]
test_expected_outputs = [
[
[10, 2],
[3, 40],
[5, 6],
[7, 88],
[9, 10]
],
[
[-1],
[-22],
[34]
],
[
[-1.3, 2.54, math.pi],
[4, '5']
],
[
[math.pi, 2, math.pi, 4, 5],
['foo', 7, 8, 'bar', math.tau],
[math.inf, 12, math.e]
]
]

test_chunk_sizes = [2, 1, 3, 5]

count = 0
for test_input_list in test_input_lists:
test_output_form_chunk_slice = chunk_with_slice(
test_input_list, test_chunk_sizes[count])
test_output_form_chunk_slice_push = chunk_slice_push(
test_input_list, test_chunk_sizes[count])
print(DIVIDER_DASH)
if test_expected_outputs[count] == test_output_form_chunk_slice and test_expected_outputs[count] == test_output_form_chunk_slice_push:
print(f'{GREEN_APPLE} Test {int(count + 1)} was successful.')
else:
print(f'{RED_APPLE} Test {int(count + 1)} was successful.')
count += 1

### JavaScript

function chunk_with_push(input_list, chunk_size) {
const output_list = [];

for (let element of input_list) {
const chunked_list = output_list[output_list.length - 1];

if (!chunked_list || chunked_list.length === chunk_size) {
output_list.push([element]);
} else {
chunked_list.push(element);
}
}

return output_list;
}

function chunk_with_slice(input_list, chunk_size) {
var start_index, end_index, chunked_list;
const output_list = [];
start_index = 0;
end_index = chunk_size;
chunked_list = input_list.slice(start_index, end_index);
output_list.push(chunked_list);
iteration = Math.floor(input_list.length / chunk_size);
if (input_list.length % chunk_size != 0) {
iteration += 1;
}

for (i = 1; i < iteration; i++) {
start_index = end_index;
end_index = chunk_size * (i + 1);
chunked_list = input_list.slice(start_index, end_index);
output_list.push(chunked_list);
}
return output_list;
}

function chunk_slice_push(input_list, chunk_size) {
const output_list = [];
let start_index = 0;

while (start_index < input_list.length) {
output_list.push(input_list.slice(start_index, parseInt(start_index + chunk_size)));
start_index += chunk_size;
}
return output_list;
}

// ---------------------------- TEST ---------------------------
divider_dash = '-----------------'
green_apple = '🍏'
red_apple = '🍎'

const test_input_lists = [
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
[1, 2, 3],
[1, 2, 3, 4, 5],
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
];
const test_expected_outputs = [
[
[1, 2],
[3, 4],
[5, 6],
[7, 8],
[9, 10]
],
[
[1],
[2],
[3]
],
[
[1, 2, 3],
[4, 5]
],
[
[1, 2, 3, 4, 5],
[6, 7, 8, 9, 10],
[11, 12, 13]
]
];

const test_chunk_sizes = [2, 1, 3, 5];

var count = 0;
for (let test_input_list of test_input_lists) {
const test_output_form_chunk_push = chunk_with_push(test_input_list, test_chunk_sizes[count]);
const test_output_form_chunk_slice = chunk_with_slice(test_input_list, test_chunk_sizes[count]);
const test_output_form_chunk_slice_push = chunk_slice_push(test_input_list, test_chunk_sizes[count]);
console.log(divider_dash);
if (JSON.stringify(test_expected_outputs[count]) === JSON.stringify(test_output_form_chunk_push) &&
JSON.stringify(test_expected_outputs[count]) === JSON.stringify(test_output_form_chunk_slice) &&
JSON.stringify(test_expected_outputs[count]) === JSON.stringify(test_output_form_chunk_slice_push)
) {
console.log(green_apple + ' Test ' + parseInt(count + 1) + ' was successful.');
} else {
console.log(red_apple + ' Test ' + parseInt(count + 1) + ' was successful');
}
count++;
}

### PHP

// Problem
// Given a list and chunk size, divide the list into sublists
// where each sublist is of chunk size
// --- Examples: (Input List, Chunk Size)     =>     Output List
// ([1, 2, 3, 4], 2)                 =>     [[ 1, 2], [3, 4]]
// ([1, 2, 3, 4, 5], 2)             => [[ 1, 2], [3, 4], [5]]
// ([1, 2, 3, 4, 5, 6, 7, 8], 3)     => [[ 1, 2, 3], [4, 5, 6], [7, 8]]
// ([1, 2, 3, 4, 5], 4)             => [[ 1, 2, 3, 4], [5]]
// ([1, 2, 3, 4, 5], 10)             => [[ 1, 2, 3, 4, 5]]
//

function builtInChunk($input_list,$input_size)
{
if ($input_size <= 0 or !is_array($input_list)) {
return false;
}
return array_chunk($input_list,$input_size);
}

// ---------------------------- TEST ---------------------------
$divider_dash = PHP_EOL . '-----------------' . PHP_EOL;$green_apple = '🍏';
$red_apple = '🍎';$test_input_lists = [
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
[1, 2, 3],
[1, 2, 3, 4, 5],
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13],
];
$test_expected_outputs = [ [ [1, 2], [3, 4], [5, 6], [7, 8], [9, 10], ], [ [1], [2], [3], ], [ [1, 2, 3], [4, 5], ], [ [1, 2, 3, 4, 5], [6, 7, 8, 9, 10], [11, 12, 13], ], ];$test_chunk_sizes = [2, 1, 3, 5];

foreach ($test_input_lists as$key => $test_input_list) {$test_output_form_chunk_slice = builtInChunk($test_input_list,$test_chunk_sizes[$key]); print($divider_dash);

if ($test_expected_outputs[$key] === $test_output_form_chunk_slice) { print($green_apple . ' Test ' . intval($key + 1) . ' was successful.'); } else { print($red_apple . ' Test ' . intval(\$key + 1) . ' was successful');
}

}

### Output

--------------------------------------------------
🍏 Test 1 was successful.
--------------------------------------------------
🍏 Test 2 was successful.
--------------------------------------------------
🍏 Test 3 was successful.
--------------------------------------------------
🍏 Test 4 was successful.

• Rather than posting redundant advice for the php snippet, apply AJNeufeld's advice about throwing and catching. An off-topic question: Why not merge this account with your Stack Overflow account? – mickmackusa Oct 16 at 5:26

## Argument Checking and Duck-typing

Two problems with this code:

    if chunk_size <= 0 or not isinstance(input_list, list):
return False

If the arguments are the correct type, the function returns a list of lists. If not, it returns False? This is going to complicate the code which uses the function. It is better to raise an exception:

    if chunk_size <= 0:
raise ValueError("Chunk size must be positive")

Secondly, you're requiring the input list to actually be a list. There are many Python types which can behave like a list, but are not instance of list. Tuples and strings are two easy examples. It is often better to just accept the type provided, and try to execute the function with the data given. If the caller provides a something that looks like a duck and quacks like a duck, don't complain that a drake is not a duck.

## Oddity

In this statement ...

chunked_list = input_list[start_index: int(start_index + chunk_size)]

... what is that int() for? It seems unnecessary.

## Return Type

You are breaking the list into multiple lists. Your return is not just a simple list; it is a list of lists. List[List[T]].

## Itertools

Python comes with many tools builtin. Check out the itertools modules. In particular, look at the grouper() recipe. It reduces your "chunking" code into 2 statements.

>>> from itertools import zip_longest
>>>
>>> input_list= [10, 2, 3, 40, 5, 6, 7, 88, 9, 10, 11]
>>> chunk_size = 2
>>>
>>> args = [iter(input_list)] * chunk_size
>>> chunks = list(zip_longest(*args))
>>>
>>> chunks
[(10, 2), (3, 40), (5, 6), (7, 88), (9, 10), (11, None)]
>>>

As demonstrated above, it produces slightly different output. The last chunk is padded with None values until it is the proper length. You could easily filter out these extra values.

>>> chunks[-1] = [item for item in chunks[-1] if item is not None]
>>> chunks
[(10, 2), (3, 40), (5, 6), (7, 88), (9, 10), [11]]
>>>

If your list can contain None values, then a sentinel object could be used instead. Revised code:

from itertools import zip_longest

def chunk_itertools(input_list: List[T], chunk_size: int) -> List[List[T]]:

sentinel = object()

args = [iter(input_list)] * chunk_size
chunks = list(zip_longest(*args), fillvalue=sentinel)
chunks[-1] = [item for item in chunks[-1] if item is not sentinel]

return chunks

JavaScript & PHP reviews left to others

You have some odd stuff going on in chunk_with_slice; specifically these lines:

def chunk_with_slice(input_list: List['T'], chunk_size: int) -> List['T']:
if chunk_size <= 0 or not isinstance(input_list, list):
return False

First, you're using strings to represent type vars (List['T']). As mentioned in the comments, strings are used to reference types that can't be referred to directly, such as needing a forward reference, or referencing something in a separate file that can't be imported. You don't need a forward reference here though. I'd just use T:

def chunk_with_slice(input_list: List[T], chunk_size: int) -> List[T]:

Second, think about those first two lines. You're basically saying "input_list is a list. But if it's not a list, return false". If you say that input_list is a list, you shouldn't be allowing other types in. You've told the type checker to help you catch type errors, so ideally you shouldn't also be trying to recover from bad data at runtime. If you expect that other types may be passed in, specify that using Union (such as Union[List, str] to allow a List and str in).

I also agree with @AJ's "It is often better to just accept the type provided, and try to execute the function with the data given." comment. I'd specify input_list to be a Sequence instead. A Sequence is a container capable of indexing/slicing and len. This covers lists, tuples, strings, and others; including user-defined types. Forcing your caller to use a specific container type is unnecessary in most circumstances.

• PEP484 allows type-hints to be given as strings, to allow forward references. – AJNeufeld Oct 16 at 13:32
• @AJNeufeld Ahh, thanks. A forward reference isn't necessary here though. I'll update my answer. – Carcigenicate Oct 16 at 14:01

For sequences (list, str, tuple, etc), this is rather straight forward:

def chunks(sequence, size):
return [sequence[index:index+size] for index in range(0, len(sequence), size)]


text:
# 4,294,967,295

(Redirected from 4294967295)
Jump to navigation Jump to search
4294967295
Cardinal four billion two hundred ninety-four million nine hundred sixty-seven thousand two hundred ninety-five
Ordinal 4294967295th
(four billion two hundred ninety-four million nine hundred sixty-seven thousand two hundred ninety-fifth)
Factorization 3 × 5 × 17 × 257 × 65537
Greek numeral ${\displaystyle {\stackrel {\mu \beta \theta \upsilon \mathrm {\koppa} \digamma }{\mathrm {M} }}}$͵ζσϟε´
Roman numeral N/A
Binary 111111111111111111111111111111112
Ternary 1020020222012211112103
Quaternary 33333333333333334
Quinary 322440024231405
Senary 15501040155036
Octal 377777777778
Duodecimal 9BA46159312
Hexadecimal FFFFFFFF16
Vigesimal 3723AI4F20
Base 36 1Z141Z336

The number 4,294,967,295 is an integer equal to 232 − 1. It is a perfect totient number.[1][2] It follows 4,294,967,294 and precedes 4,294,967,296. It has a factorization of ${\displaystyle 3\cdot 5\cdot 17\cdot 257\cdot 65537}$. Since these factors are the five known Fermat primes, this number is the largest known odd value n for which a regular n-sided polygon is constructible using compass and straightedge.[3][4] Equivalently, it is the largest known odd number n for which the angle ${\displaystyle 2\pi /n}$ can be constructed, or for which ${\displaystyle \cos(2\pi /n)}$ can be expressed in terms of square roots.

## In computing

The number 4,294,967,295, equivalent to the hexadecimal value FFFF,FFFF16, is the maximum value for a 32-bit unsigned integer in computing.[5] It is therefore the maximum value for a variable declared as an unsigned integer (usually indicated by the unsigned codeword) in many programming languages running on modern computers. The presence of the value may reflect an error, overflow condition, or missing value.

This value is also the largest memory address for CPUs using a 32-bit address bus.[6] Being an odd value, its appearance may reflect an erroneous (misaligned) memory address. Such a value may also be used as a sentinel value to initialize newly allocated memory for debugging purposes.

## References

1. ^ Loomis, Paul; Plytage, Michael; Polhill, John (2008). "Summing up the Euler φ Function". College Mathematics Journal. 39 (1): 34–42. JSTOR 27646564.
2. ^ Iannucci, Douglas E.; Deng, Moujie; Cohen, Graeme L. (2003). "On perfect totient numbers" (PDF). Journal of Integer Sequences. 6 (4): 03.4.5. MR 2051959.
3. ^ Lines, Malcolm E (1986). A Number for your Thoughts: Facts and Speculations About Numbers from Euclid to the latest Computers... (2 ed.). Taylor & Francis. p. 17. ISBN 9780852744956.
4. ^
5. ^ Simpson, Alan (2005). "58: Editing the Windows Registry". Alan Simpson's Windows XP bible (2nd ed.). Indianapolis, Indiana: J. Wiley. p. 999. ISBN 9780764588969.
6. ^ Spector, Lincoln (19 November 2012). "Why can't 32-bit Windows access 4GB of RAM?". PC World. IDG Consumer & SMB. Archived from the original on 5 March 2016.


text:
# Creating a Test Installation

Creating a Test/Development Installation When a new version of vBulletin comes out, there’s always a clamour for people to be one of the first up and running with the latest version. While in the case of bug fixes, the need to upgrade quickly is understandable, too often people don’t consider what effect an upgrade will have on their site. The following is aimed at providing enough knowledge to be able to create a test ‘mirror’ of a site so that a test of an upgrade (or any change for that matter!) can be made.

## Step 1 - Update URLs and Backup your database!

An all important step in any upgrade but without it, you’ll never be able to test an upgrade - period! As you’re going to be moving your database to be read by software on a different URL, you need to make sure you update the database to reflect this. There are two ways to do this:

1. Update the URLs before backing up the database or
2. Update manually in the database after backing up (NOT RECOMMENDED)

To update the URLs before backing up, follow these simple steps:

Close your site via AdminCP > Settings > Options > Turn Your vBulletin On and Off
Update the URLs at AdminCP > Settings > Options > Site Name / URL / Contact Details
Warning:
***DO NOT CLOSE YOUR BROWSER AFTER THE ABOVE STEP***
Update the URLs at AdminCP > Settings > Options > Site Name / URL / Contact Details back to your live URLs

This will give you a ready made backup that will require no manual intervention to ensure that it’s ready for testing against.

There are a number of ways to backup your database. The most reliable method of backing up and restoring a database is with shell access via ssh. This is because backing up with a PHP script like phpMyAdmin can result in PHP timeouts errors and an incomplete backup file. For more information on how to do this, please see the instructions here:

If you don’t have shell access, some people have also reported success with these scripts:

MySQLDumper: http://www.mysqldumper.de/en/index.php

Bigdump: http://www.ozerov.de/bigdump.php

Once you have your backup, you need to actually restore it to be able to test against it.

## Step 2 - Restore your database

There’s two options here depending on the hosting package you have:

Create a new database and restore to it or

Option 1, if you have more than 1 database available to you, is the option we’d recommend in every case because quite simply, it’s the safest! That said, some hosting plans, particularly lower costed shared plans, may only allow a user 1 database so you may have no choice but to go with option 2!

Option 1 - Create a new database and restore to it

This is the safest way to go. From your server’s control panel, create a new database then restore your freshly backed up database into this new database. As this is a completely separate database to your live one (different database name and hopefully different login details), there will be no need to manipulate the database prior to using it.

Option 2 - Restore into your live database

While this is NOT recommended, there are a number of users who will simply have to go down this route due to the lack of features with the hosting package they have (or can afford). Before doing this, make sure you read these steps BEFORE attempting to do the restore.

To do these, you will need to have a text editor installed. Windows users will have Notepad and Wordpad, Mac users may have TextEdit. I’ve used Wordpad without issue - and it’s Find and Replace tool will be needed for the following steps as you will need these to manipulate the database backup before restoring it but don’t worry - it’s not complicated as you’ll see…

a. Table prefixes

Whether you have prefixes or not, you are going to need to create a prefix to distinguish your test database from your live one. The following shows a table with no prefix then one with a prefix of ‘vb_’ - the rest of this entry will assume that prefix is currently used:

No Prefix:

DROP TABLE IF EXISTS access; CREATE TABLE access ( userid int(10) unsigned NOT NULL default ‘0’, forumid smallint(5) unsigned NOT NULL default ‘0’, accessmask smallint(5) unsigned NOT NULL default ‘0’, PRIMARY KEY (userid,forumid) ) ENGINE=MyISAM DEFAULT CHARSET=latin1;

With Prefix:

DROP TABLE IF EXISTS vb_access; CREATE TABLE vb_access ( userid int(10) unsigned NOT NULL default ‘0’, forumid smallint(5) unsigned NOT NULL default ‘0’, accessmask smallint(5) unsigned NOT NULL default ‘0’, PRIMARY KEY (userid,forumid) ) ENGINE=MyISAM DEFAULT CHARSET=latin1;

To ensure your test database is unique, you’re going to need to add/change the prefix depending on what you currently have in place. Using the ‘Find and Replace’ option in your editor, you can add/change the prefix very easily (note if you have no prefix you will need to do this twice - once to edit the ‘Drop’ command, once for the ‘Create’ one):

Once, you hit OK/Replace All or whatever command your editor has, this will go through and add/replace prefixes on all tables. Now save this file under a different name on your local machine.

Now that you have your edited database, upload this to your server then restore it. For more instructions on using ssh, see this section of the manual:

http://www.vbulletin.com/docs/html/maintenance_ssh_restore

This will create a new set of duplicate database tables within their own ‘group’ thanks to the amended prefix.

## Step 3 - Files

So, you’ve got your database in place so all we need is to upload the files - right? Nearly! Yes, you will need to have an actual installation of vBulletin on your server to use these but it’s not just a case of uploading the files and away you go - so read on and follow…

First thing’s first, create a new empty directory on your server called ‘testvb’. You will need to protect this directory from the general public. The most common way to do this is by a combination of .htaccess and .htpasswd files. For more on these and assistance in setting these up, go to:

http://www.htaccesstools.com/htpasswd-generator/

Some Windows Server users may find that this doesn’t work for them in which case you should use the permissions tools available on the server

Next, you need to decide what you’re doing. Are you testing some changes to the templates etc. without upgrading or are you testing an upgrade?

1. Testing changes

If you’re only testing some changes you want to make to the site (new styles, template changes) then either copy your live site’s files to the ‘testvb’ directory or download a copy of your live site and then upload them into the ‘testvb’ directory.

If you’re testing an upgrade, then there’s no need to copy your live site’s files as you’re only going to be overwriting them with the newer ones anyway! In this instance, simply download the new files from the Members Area and upload these to your ‘testvb’ directory.

1. config.php

VERY IMPORTANT STEP! I highlight this as without this step, you’ll be doing whatever you do to your live database!

Open config.php in your normal web editor. Again, this will vary slightly depending on whether you’re using a different database or whether you’re having to use different prefixed tables in the same one.

a. Imported Database to a new database

If you’ve got the luxury of using a completely separate database, then you will need to edit the following details to ensure you’re pointing to the correct one:

Database Name

b. Imported Database to different prefixed tables in live database

This is even more important in this scenario. You need to edit the following areas:

Database Table Prefix

Why edit the cookie prefix? If you’re using the same Cookie prefix on your test site as you do on your live site, your browser won’t distinguish which site you’re actually viewing as they’re both on the same domain. This will cause problems when logging in and doing anything where your personal settings are saved in a Cookie. The easiest way to distinguish these is to change the test site’s value to ‘vbtest’.

Regardless of which method of database import you’ve had to do, you should add the following to the top of the config.php file, right under <?php:

define(‘DISABLE_MAIL’, 1);

This will stop the vBulletin email system from sending mails to users on their birthdays, if you add a test post to a subscribed thread etc. The last thing you want is users emailing you to say they’ve had a notification from a strange URL that looks like it could be your site…


text:
Public Group

vb.net 2003 writting to a file with a size limit

This topic is 4531 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

Recommended Posts

I'm trying to chunck up files that are larger then 2048 bytes into files less then 2048 bytes, but I am having a problem doing this. Is there a way with System.IO.StreamWriter to keep track of the data writtin? I tried to do it manually, but it only works about 60% of the time. Here is what I have now if anyone can find a flaw in my function.
'This is the input file that we are reading from (The book that we are getting all the data).s
Private m_InputStream As System.IO.StreamReader = Nothing

'This is the Currently open file that we are writing to.
Private m_OutputStream As System.IO.StreamWriter = Nothing

Private Sub m_Create_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles m_Create.Click
'This is what we're reading from the file
Dim strStringRead As String = ""

Dim iDataWritten As Integer = 0

'This is what we're going to be writting to the file
'Dim strStringToWrite As String = ""

Try
While Me.m_InputStream.Peek <> -1

'If the total size of the string is less then 2048 bytes (2 KB) then add and read the next line,
'other wise we must stop and write.
If (strStringRead.Length < Me.m_kMaxFileSize) Then
Else
'the string needs to be chuncked
End If

End While
Catch ex As Exception

End Try

End Sub

'This function will create the File and write the table of contents
Private Sub WriteData(ByVal strStringToWrite As String, ByRef iDataWritten As Integer)
Try
If ((iDataWritten + strStringToWrite.Length + 1) >= Me.m_kMaxFileSize) Then
iDataWritten = 0

Me.m_OutputStream.Close()
Me.m_OutputStream = Nothing
End If

If Me.m_OutputStream Is Nothing Then
Dim strFilename As String = New String(Me.m_OutputFile.Text + "\" + "page" + CType(Me.m_iPageNumber, String) + ".txt")
Me.m_OutputStream = New System.IO.StreamWriter(strFilename, False, System.Text.Encoding.ASCII)

Me.m_iPageNumber += 1
End If

'Dim strFilename As String = New String(Me.m_OutputFile.Text + "\" + "page" + CType(Me.m_iPageNumber, String) + ".txt")
'Dim OutputStream As System.IO.StreamWriter = New System.IO.StreamWriter(strFilename, False, System.Text.Encoding.ASCII)

Me.m_OutputStream.WriteLine(strStringToWrite)
'add one for newline characters
iDataWritten += strStringToWrite.Length + 1

Catch ex As Exception

End Try
End Sub

EDIT: Private Const m_kMaxFileSize As Integer = 2048 that should've been in there too. thanks in advance, ~guyaton

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text:
# Set theory strange union with cross product

I don´t know what property of sets is being used in this exercise:

Sets:

$$A = \{4, 5, 6, 7\}$$

$$B = \{6, 8\}$$

$$C = \{4, 7, 9\}$$

Determine: $$A \cup (B \times C)$$:

I just did $$B \times C$$ and but I don't understand how can you make union between a set and another set but with ordered pairs.

Also, I have a set $$A$$ and another one $$B, \vert B \vert = 3.$$ I need to obtain $$\vert A \vert$$ based of the fact that there are $$4096$$ relations between $$A$$ and $$B$$. I did $$\vert A \times B \vert = \vert A \vert \vert B \vert = 4096$$ but when I get $$\vert A \vert$$ it makes no sense because $$\vert A \vert$$ would be $$1365.33.$$

I hope someone can help me, I would appreciate it a lot. Thanks.

• For example, $A=\{a,3,e\}$ and $B=\{(1,0),(\alpha,x)\}$, then $$A\cup B=\{ a,3,e,(1,0),(\alpha,x)\}$$ Sep 23 '19 at 2:40
• To help with the relation question, all relations between $A$ and $B$ are actually subsets of $|A \times B|$. How many subsets are there of a given set? Sep 23 '19 at 2:42
• Just like that?! Hahaha, I was overcomplicating myself. Thanks!! Sep 23 '19 at 2:42
• @AnthonyTer You mean subsets of $A\times B$; $4096$ is the size of the number of subsets of $A\times B$. Sep 23 '19 at 4:40

If $$A = \{apples, oranges, bananas\}$$ and $$B= \{3,7,9\}$$ then $$A\cup B = \{apples, oranges, bananas,3,7,9\}$$.

There is no restriction that if $$A$$ is a set of fruit that the only things you can do with it is in the realm of fruit nor that if $$B$$ is in the realm of numbers that the only things we can do with it are in the realms of numbers.

$$A = \{4,5,6,7\}$$ in the realm of single numbers.

And $$B\times C =\{(6,4),(6,7),(6,9),(8,4),(8,7),(8,9)\}$$ in the real of ordered pairs

And so $$A \cup (B\times C) =\{4,5,6,7,(6,4),(6,7),(6,9),(8,4),(8,7),(8,9)\}$$ which is not restricted to either the ream of number nor the realm of ordered pairs.

.....

As for relations. Note: one relation is subset of $$A\times B$$. A relation is not an element of $$A\times B$$.

Example if $$A = \mathbb N$$ and $$B=\mathbb N$$ and the relation is "the first number divides the second" then "the first number divides the second" $$\ne (a,b)$$ for any one pair $$(a,b)$$.

Instead "the first number divides the second" $$= \{(1,2),(5,15), (7,35),,.......\}$$ which is a whole subset of ordered pairs.

So if $$C= \{1,5\}$$ and $$D=\{2,3,5\}$$

Then what are the possible relations.

First is: $$\emptyset$$. That is no number is related to any other.

The second is $$\{(1,2)\}$$. That is $$1$$ is related to $$2$$ but nothing else are.

Another is $$\{(1,2),(1,5), (5,3),(5,2)\}$$. Which is a arbitrary $$1$$ is relateed to $$2$$ and $$5$$ and $$5$$ is related to $$3$$ and $$2$$. Why? Who cares?

The last is $$\{(1,2),(1,3),(1,5),(5,2),(5,3),(5,5)\} = C\times D$$. Everything is related to everything!

So how many total relations are there?

Well every subset of $$C\times D$$ can be a relation. so if $$\mathscr P(C\times D)=\{$$ the subsets of $$C\times D\}$$ then the number of relations is $$|\mathscr P(C\times D)|$$.

Which is a different concept then $$|C\times D|$$.

....

So you figure that if $$|A| = k$$ and $$|B| =3$$ then $$|A\times B| = 3k$$. That's fine.

But $$4096 = |\mathscr P(A\times B)|$$.

So you need to figure out if $$|A\times B| = 3k$$ then what does $$|\mathscr P(A\times B)| = f(3k)$$ is.

Can you?

Hint: If I eyeball factor $$4096$$ I get that $$4|4096$$ so $$4096 = 4*1024$$ and if I eyeball factor $$1024$$ I see it is divisible by $$2$$ so $$4096 = 8*512$$ and if I eyeball factor I get .... hey, wait a minute!

You are on the right track, Andres. Given $$A=\{4,5,6,7\},$$ $$B=\{6,8\},$$ $$C=\{4,7,9\},$$

$$B \times C = \{ (6,4), (6,7), (6,9), (8,4), (8,7), (8,9) \}$$.

The fact that the members of $$B \times C$$ are ordered pairs does not affect the union operation. We still end up with another set whose members belong to $$A$$ or $$B \times C$$ or both.

Hence, $$A \cup (B \times C) =\{4,5,6,7,(6,4), (6,7), (6,9), (8,4), (8,7), (8,9)\}$$

Note that when you draw a comparison between $$6\in A$$ and $$(6,7)\in B \times C$$, you are not drawing a comparison with anything inside the ordered pair. We are drawing a comparison between MEMBERS of $$A$$, which are the integers $$4,5,6,7$$, and the MEMBERS of $$B\times C$$, which are the ordered pairs themselves. The integer $$6$$ is not the same as the ordered pair $$(6,7)$$ - even though the ordered pair contains $$6$$. The two are fundamentally different "things," so we include $$6$$ in our union and we also include $$(6,7)$$ in our union.

As for your question re the relation... we are given sets $$A$$ and $$B$$ s.t. $$|B|=3$$ and we know there are $$4096$$ relations between $$A$$ and $$B$$. There are a few things you need to be aware of in order to solve this:

(1) Definition of a relation, a subset, a Cartesian product, and a powerset.

(2) How to determine the cardinality of a Cartesian product and a powerset.

Recall that a relation from $$A$$ to $$B$$ is a subset of $$A \times B$$. We are told there are $$4096$$ possible relations; in other words, there are $$4096$$ possible subsets of $$A \times B$$.

Recall that a powerset of some set $$S$$, denoted as $$\mathfrak{P}(S)$$, is the set of all subsets of $$S$$ and has a cardinality of $$2^n$$ where $$|S|=n$$. Hence, if there are $$4096$$ possible subsets of $$A \times B$$, then that means the set of all subsets of $$A \times B$$, or the $$\mathfrak{P}(A \times B)$$, has a cardinality of $$4096.$$ In other words, $$|\mathfrak{P}(A \times B)|=4096.$$

And, if $$|A \times B|=n$$, then $$|\mathfrak{P}(A \times B)|=4096=2^n$$. We now have an equation we can work with.

Now, also recall that $$|A \times B|=|A| \cdot |B|$$. We know $$|B|=3$$, so $$|A \times B|=|A| \cdot 3$$. In addition, we have already established that $$|A \times B|=n$$, so $$n=|A| \cdot 3$$. By substitution with $$n$$, we have

$$2^n=2^{|A|\cdot 3}=4096$$. Now we can solve for $$|A|$$ to obtain the answer to the problem.

$$|A|=(\log_24096)/3=4$$