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.
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. 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. Directions Click on the sliders to adjust the input voltage, and the number of windings on the primary and secondary coils. Alter the input voltage and describe how the sine-wave graph changes to illustrate the voltage magnitude.