Transformers are used to increase or decrease AC voltages and currents in circuits. The operation of transformers is based on the principal of mutual inductance. A transformer usually consists of two coils of wire wound on the same core. The primary coil is the input coil of the transformer and the secondary coil is the output coil. Mutual induction causes voltage to be induced in the secondary coil.

Click on the sliders to adjust input voltage and number of windings on the primary and secondary coils.

As you adjust the number of windings of the coils, notice that the input and output voltages are directly proportional to the number of windings of the coils.

Voltage is determined by the following formula:

where V_I is the input voltage of the primary coil, V_O is the output voltage of the secondary coil, N_P, the is number of windings of the primary coil, and N_S is the number of windings in the secondary coil.

If the output voltage of a transformer is greater than the input voltage, it is called a step-up transformer. If the output voltage of a transformer is less than the input voltage it is called a step-down transformer.