Hand cranked radios and flashlights are powered by enery created by agitating a magnet around a metal coil. The crank is use to rotate the magnet ultimately creating a dynamo generator. Cranking generally allows for the creation fo more energy than shaking, another popular method of powering handheld devices without batteries. The energy created by cranking or shaking is stored in a capacitor or rechargeable battery.

Michael Faraday created the direct current generator in 1830. He realized that by rotating a coil inside of a magnetif field the voltage of the current produced increases according to the number or amount of turns of the wire inside the coil. This principle later led to the invention of the electric motor.