An equivalent circuit is one that produces the same voltage and current to a given load as the original circuit that it replaces.

The superposition theorem is useful for circuit analysis only in ac circuits.

A Thevenin ac equivalent circuit always consists of an equivalent ac voltage source and an equivalent capacitance.

Norton's theorem provides a method for the reduction of any ac circuit to an equivalent form consisting of an equivalent voltage source in series with an equivalent impedance.

One circuit is equivalent to another, in the context of Thevenin's theorem, when the circuits produce the same voltage.