Superposition can only be applied to networks that are linear and bilateral. Fortunately, all of components we have discussed; resistors, capacitors and inductors, fall into that category. Further, superposition cannot be used to find values for non-linear functions, such as power, directly.

In which circuit superposition theorem can be applied?

It is used in converting any circuit into its Norton equivalent or Thevenin equivalent. The theorem is applicable to linear networks (time varying or time invariant) consisting of independent sources, linear dependent sources, linear passive elements (resistors, inductors, capacitors) and linear transformers.

What is condition under which the superposition theorem can be applied?

All the components of the circuit must be linear. For example, in a resistor, the current must be proportional to the applied voltage. Another example of the linear circuit is that in an inductor, current and flux linkage must be proportional.