Kirchhoff’s Laws
Kirchoff’s current law or point law (KCL)
Statement:-
In any electrical network, the algebraic sum of the currents
meeting at a point is zero.
Σ I = 0 ……………………at a junction or node
Assumption:-
Incoming current = positive
Outgoing current = negative
Kirchoff’s voltage law or mesh law (KVL)
Statement:-
The algebraic sum of the products of currents and resistances in
each of the conductors in any closed path (or mesh) in a network plus the
algebraic sum of the emfs in that path is zero.
Σ IR +Σemf = 0 …………………………..round the mesh
Assumption:-
-
Rise in voltage (If we go from negative terminal of the battery to positive terminal) = positive
-
Fall in voltage (If we go from positive terminal of the battery to negative terminal) = negative
-
If we go through the resistor in the same direction as current then there is a fall in potential. Hence this voltage is taken as negative.
-
If we go through the resistor against the direction of current then there is a rise in potential. Hence this voltage drop is taken as positive.
Example:-
Write the loop equation for the given circuit below
Solution:
Apply KVL to the loop,
