Electric motor. This consists of a loop of wire that is free to rotate in a magnetic field (yellow arrows). The loop is attached to a power source (left), which drives a current (blue arrows) around the wire. The loop is connected to the power source through a commutator, a pair of half rings, which reverses the flow of current when the loop has rotated through 180 degrees, keeping it rotating in the same direction. As well as an electric current producing movement, movement of a wire in a magnetic field produces an electric current. This principle is used in the generators that provide electricity in power stations.