Transformer Circuit Review: Ideal Transformers, Conservation of Energy

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:

Pout=Pin

n2/n1=V2/V1

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

The output voltage Vout=N*Vin.

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:

            Zout = Vout/Iout = (N*V­in)/(Iin/N) = N2 * Zin

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