Induction charging (electromagnetic induction) is a type of wireless charging that uses electromagnetic fields to transfer energy between two objects. It is a method of charging an object, usually a battery, without making physical contact with a charger. Induction charging works by using two coils, a transmitter coil and a receiver coil, which are separated by a small air gap. An alternating current (AC) flows through the transmitter coil, generating a changing magnetic field. This changing magnetic field induces an electromotive force (EMF) in the receiver coil, which causes an AC current to flow in the receiver coil. The receiver coil is connected to the device battery, which is thus charged. Induction charging is often used in electric toothbrushes, smartphones, and other portable devices.