Electromagnetic induction is important to humans because it is useful. SAT II Physics has been known to ask questions about real-world applications of electromagnetic induction. The two most common applications are the electric generator and the transformer.

The electric generator, sometimes called a “dynamo,” is a noisy favorite at outdoor events that need electricity. It uses the principle of electromagnetic induction to convert mechanical energy—usually in the form of a gas-powered motor—into electrical energy. A coil in the generator rotates in a magnetic field. As the magnetic flux through the coil changes, it induces an emf, creating a current.

The transformer converts current of one voltage to current of another voltage. A simple transformer consists of two coils wrapped around an iron core. Transformers rely on the property of mutual induction: the change in current in one coil induces an emf in another coil. The coil with the applied current is called the primary coil, and the coil with the induced emf is called the secondary coil.

The induced emf is related to the emf in the primary coil by the number of turns in each coil:

Outside a power plant, a “step-up” transformer, whose primary coil has fewer turns than its secondary coil, increases the voltage (emf) of the current that is transported along power lines. Then, before the power enters your house, a “step-down” transformer, whose secondary coil has fewer turns than its primary coil, reduces the voltage. The higher voltage on power lines cutting across the countryside allows more electricity to be transported quickly to urban centers. The lower voltage within your house renders the electricity safer.