suppose while shopping you go cash less
and your parents use cards the
shopkeeper always scans or swipes the
cards shopkeeper does not take a photo of
the card or tap it why does he swipe or
scan it and how does this swiping deduct
money from the card this happens because
of the electromagnetic induction
This is the famous michael faraday faraday
noticed that when he moved the permanent
magnet in and out of a coil or a single
loop of wire it induced an electromotive
force or EMF in other words a voltage
and therefore a current was produced off
this led to a very important law linking
electricity with magnetism Faraday's law
of electromagnetic induction so how does
this work when the magnet shown here is
moved towards the coil the pointer of
the galvanometer will deflect away from
its position in one direction only and
if the magnet is moved away from the
coil the needle of the galvanometer
deflects in the opposite direction
indicating a change in polarity
or we can keep the magnet fixed and move
the coil both will produce electric
current in the coil which lights up the
bulb
you
now the magnitude of EMF produced
depends upon rate of change in magnetic
flux density which is d Phi by DT now it
is seen that if number of windings of
the coil is increased then the EMF is
increased so the EMF is directly
proportional to N or the number of turns
this this is the formula we finally get
be equals to minus n multiplied by D Phi
by DT
you
capital e is here basically the EMF
the negative sign comes from the fact
that the EMF induced in the coil acts to
oppose any change in the magnetic flux
this is summarized in Lenz's law which
states that the induced EMF generates a
current that sets up a magnetic field
which acts to oppose the change in
magnetic flux another definition states
that the direction of induced current is
such that it opposes very cause that
produces it now let us learn how to
determine the direction of induced
current through Fleming's generator law
suppose there is a magnet RR let it be
horseshoe magnet whose two poles are
shown as the North Pole and the South
Pole
so suppose there is a horseshoe magnet
whose two poles are shown here so we all
know that the magnetic lines of force
are from the North Pole to the South
Pole of the magnet magnetic lines of
force are also called the magnetic flux
the Fleming's right-hand rule or the
generator rule can be used to find the
direction of induced current when a wire
loop passes through a field
perpendicular to it now take your right
hand and stretch your forefinger middle
finger and thumb perpendicular to each
other
let the forefinger point towards the
direction of the magnetic field or flux
and thumb point towards the motion of
the loop or the magnet just like this
then Fleming's law states that the
direction in which the middle finger
points is the direction of the induced
current in the wire so in this way we
can find the direction of induced
current if we push through the wire in
the opposite direction the direction of
the electric current just reverses
immediately pause the video and try it
out yourself remember it should be your
right hand not your left hand
now I will discuss about the alternating
current or AC generator sir AC generator
consists of a rectangular coil known as
armature this armature is rotated
rapidly between the poles of a permanent
magnet horseshoe magnet the ends of the
rectangular coil are connected to the
two circular metal pieces called slip
rings the slip rings rotate along with
the coil the two pieces of carbon
brushes b1 and b2 are kept in contact
with the slip rings the carbon brushes
are capable of tapping the current
produced in the rotating coil suppose
the axle is rotated clockwise so the
coil also rotates clockwise side a B of
the coil moves up inside C D moves down
now you know just apply Fleming's
right-hand rule on a be certain the
direction of the force is upwards and
the direction of magnetic field is
towards the right so the direction of
current induced electric current is into
the paper from A to B
next port on CD is downwards magnetic
field is from left to right so the
current is going from C to D thus in
this case the current moves through the
path ABCD and moves from b2 to b1 in the
external circuit after half a rotation
the position of a B and C D reverses
then just apply Fleming's right-hand
rule again and you will get that the
current moves through the path dcba
check it out yourself since the
direction of current reverses after half
a rotation or 180 degree this current
which is produced is known as
alternating current so basically this is
alternating current generator or AC
generator
it is a moving coil type microphone
which uses electromagnetic induction to
convert the sound waves into an
electrical signal it has a very small
coil of thin wire suspended within the
magnetic field of a permanent magnet as
the sound wave hits the flexible
diaphragm the diaphragm moves back and
forth in response to the sound pressure
acting upon it causing the attached coil
of wire to move within the magnetic
field of the magnet the movement of the
coil within the magnetic field causes a
voltage to be induced in the coil is
defined by Faraday's law of
electromagnetic induction the resultant
output voltage signal from the coil is
proportional to the pressure of the
sound wave acting upon the diaphragm
that allowed for stronger the sound wave
the larger the output signal will be
making this type of microphone design
pressure sensitive
