commutator

The arrangement of contact points in an electric motor connecting an external direct current power supply and the rotating electric coils that use the power, used to generate the AC voltages needed by the coils. The commutator is located at the rotating shaft of the motor, where two power contacts are swept underneath two metal brushes, supplying positive and negative voltage to the coils. When the motor has rotated 180 degrees, the power contacts are each moving under the opposite brush, reversing the polarity of the voltage supplied to the coils.

In a group or an algebra, an element of the form ghg^-1h^-1 where g and h are elements of the group or algebra. If g and h commute, the commutator is the identity element. The commutator is often written [g, h].