Let's have a discussion on superposition theorem. If there are several sources of EMFs acting
simultaneously in an electrical circuit, according to superposition theorem, EMF of each source
acts independently of those of other sources, i.e. as if the other sources of EMF did not
exist, and the current in any branch of the network is equal to each source of EMF separately
All EMFs being taken to zero. This theorem is only applicable in linear circuits, that
are circuits consisting of resistances in which Ohm's law is valid. Here in this circuit
there are two voltage sources V1 and V2 acting simultaneously on the circuit. Because of
these two voltage sources, say current i flows through the resistance R. Now replace V2 by
short circuit, keeping V1 at its position and measure current through the resistance
R, say it is i1. Then replace V1 by short circuit, reconnect V2 to its original position
and measure current through the same resistance R and say it is i2. Now if we add these two
currents i1 and i2, we will get the current which is equal to the current that was actually
flowing through R when both voltage sources V1 and V2 were acting on the circuit simultaneously
Thank you