Hello friends in this video we are going
to see the most fundamental law along
with the Ohm's law that we are supposed
to use to solve a numerical not only a
numerical but lots of concepts are based
on these law so the law is kirchoff's
voltage law also known as KVL law states
that algebraic sum of all the potential
difference in a loop is always equal to
zero so I repeat algebraic sum of
potential differences in a closed loop
circuit that in a closed circuit is
equal to zero again the important
concepts over here algebraic sum and
what is the meaning of closed circuit so
to elaborate this I will consider a
simple circuit like this so I am having
two batteries and three resistances
connected in series like this so
obviously it is a closed circuit and
current will flow and because of this
current there will be potential drop or
voltage drop across these three
resistances anyways these are the
batteries having fixed polarities like
this so we have to elaborate the concept
of algebraic sum of potential
differences so here in
all I'm having one two three four five
elements each element is having some or
other voltage drop or it can also be
called as voltage rise so I will right
over here two concepts voltage drop and
voltage rise so voltage drop I will
consider as negative value and voltage
rise I will consider as positive value
now understand the meaning and
difference between voltage drop and
voltage rise suppose there is one
element connected between these two
point it could be anything it could be a
battery or it could be a resistance and
if in the direction of current if the
two terminals having the polarities plus
minus in the direction of current
meaning the polarity is changing from
plus to minus so whenever it is changing
from plus to minus I will consider that
particular potential as voltage drop
likewise if in a direction of a current
or pressing a closed circuit if I am
having element voltage polarity changing
from minus to plus it could be anything
either a resistance or a battery I will
consider that particular potential as
voltage rise so lets apply this
concept to the circuit now I am
considering loop a b c d and if i
tracing a part from a b c d
back to the a I can have one two
three four five potential differences so
let's start with r1 so in this direction
it is changing from plus to minus plus
to minus I consider as a voltage drop
and I will consider that particular
value as negative so for this resistance
so voltage drop I will write as minus I
into r1 current flowing through the r1
is I resistance values r1 so I to r1 is
a voltage or a potential same way for r2
in this direction I am having plus to
minus plus to minus is again a voltage
drop which is a negative so minus I R2
third again a resistance having the same
polarity plus minus so I will get minus
I R3 now pay attention in the direction
of current Here I am tracing all the
voltage drops like this I am having plus
minus once again plus minus so it is a
voltage drop but hold on
it is not a resistance it is a fixed
voltage battery so I will have a minus
sign because it is plus 2 minus but I
should not write I into into in fact I
should write only e 2 because that is a
fixed voltage I am having irrespective
of amount of current and finally in the
direction of current I am having last
potential as minus plus minus plus is
voltage rise so voltage rights should be
denoted Plus and mind you it is a
battery so it will have simply plus e 1
equals to 0 so ultimately I can say
these two are the battery voltages which
I can Club together even minus e 2 equal
to this 3 IR 1 IR 2 IR 3 are the voltage
drops so I can write here
I R1 plus I R2 plus I R3 so ultimately
what is happening all the potential and
amount of energy will remain conserved
so KVL can also be considered as
conservation of energy so batteries need
to spend some energy and same energy
will be consumed by all the resistors
connected in a circuit so here we come
to an end of a most fundamental law that
is KVL from which we turn able to solve
a problem which we will see in a
subsequent videos thank you
