**Equivalent voltage and current sources are equivalent – if you are replacing one with another and the rest of the circuit response is the same.**

There are equivalent current and voltage sources shown in figure (in the nodal analysis post), producing* ${I}_{1}$*, and $U$ the same current and voltage is applied to the rest of the circuit. Their equivalence condition is described by the formula * $U=Z*I$*, where *$Z$* is an internal complex resistance of both current and voltage sources.

The voltage on the voltage source terminals goes by the resistor voltage subtracted from EMF $E$. And the voltage on the current source terminals is equal to the voltage on the resistor $({I}_{1}\u2013I)$ with the complex resistance as *$Z$*. In both cases $U=E\u2013{I}_{1}Z=Z(I\u2013{I}_{1})$. It means we are getting the condition of source equivalence.

However, the power of both current and voltage sources are different. Voltage source power is equal to* ${\left|Z{I}_{2}\right|}^{2}$*, power consumed on the current source is *${\left|Z({I}_{1}\u2013I)\right|}^{2}$*. It means the equivalence of current and voltage sources has to be used only in terms of unchangeable currents, voltages and powers.