let us talk about superposition theorem
an electrical circuit does not always contain a single source of supply
it may contain more than one source of supply. the sources of supply may be either voltage sources
or current sources, or both voltage, and current sources
there is a special type of circuit solving method for such circuits that contain more than one source of supply
here, the effect of each source is calculated separately, and the combined effects of all the sources are taken into consideration
here, the effect of each source on a particular branch of a network is calculated first separately
then, we have to add all effects on that branch of the circuit
the sum of the effects gives the actual effect on the branch when all the sources are acted on the circuit
the superposition theorem states that in a linear network containing more than one source
the current flowing in any branch is the algebraic sum of currents that would have been produced by each source taken separately
with all the other sources replaced by their respective internal resistances. in case, the internal resistance of a source is not provided, the voltage sources will be short-circuited
and current sources will be open-circuited. to clarify the concept, let us take an example
using the superposition theorem
let us find the value of current, in the branch BD in the circuit
we shall consider each source separately, and calculate the current flowing through the branch BD
for that, first the 24 volt source is taken by short-circuiting the 12 volt source, as shown here
now, by applying any simple circuit law, we will find that the current through the branch BD is, 4 by 3 ampere
now, consider the 12 volt source, and short-circuit the 24 volt source as shown
now, by applying any simple circuit law, we will find that the current through the branch BD is, 2 by 3 ampere
sum of these two currents would be 4 by 3 plus 2 by 3, that is 2 ampere
after, taking both sources into circuit. let us calculate the current through the branch BD
by applying any simple circuit law, we will find that the current through the branch BD is, 2 ampere
so, it is proved that, the current flowing through the branch is the algebraic sum of currents that would have been produced by each source taken separately, with all the other sources replaced by their respective internal resistances
this is superposition theorem. hope, you got the concept. thank you