Electromagnetic induction is the creation of an electrical voltage – or potential difference – across a conductor within a changing magnetic field.
When a conductor cuts across a magnetic field, current flows in the conductor. It flows one way when the conductor cuts the field in one direction, then reverses as it cuts the field in the opposite direction.
The current is called alternating, because it flows one way, and then the other. The term alternating current is often shortened to AC. That's the sort of electrical energy that comes through power outlets. It's also produced by an alternator, as the name indicates.
Moving a wire inside a magnetic field produces a current flow. Similarly, moving a magnet inside a stationary coil of wire, produces the same effect.
If a magnet is rotating in an iron yoke, and a coil of wire is wound around the stem of the yoke to form a complete circuit with the ammeter, this will indicate if current flows.
As the magnet rotates, the ammeter deflects for current flow. For every half-revolution, current flow reverses. Increasing the speed of the magnet increases the amount of electrical energy produced. Electromagnetic induction is applied in alternators and ignition coils.