In a closed system, energy can be transferred through different forms (heat, kinetic energy, potential energy, etc), but not created nor destroyed. For a passive device such as a transformer, the energy in the system must also follow. This is termed conservation of energy.

A transformer is a passive circuit component which follows these basic formulas, where P is the power and n is the number of turns on the transformer:

P_{out}=P_{in}

n_{2}/n_{1}=V_{2}/V_{1}

**Consider an electrical transformer with turns ratio N, what is the output voltage? What is the output current?**

The output voltage V_{out}=N*V_{in}.

A correct answer to this question must satisfy that power is conserved. This means that the output power must equal the input power. Power = voltage * current.

The impedance of the transformer for N turns ratio:

Z_{out} = V_{out}/I_{out} = (N*V_{in})/(I_{in}/N) = N^{2} * Z_{in}