The d.c. motor — Describe

Describe how a simple electric motor operates, including the role of the split-ring commutator and brushes.

A current-carrying coil is placed between the poles of a magnet; since the current flows in opposite directions along the two sides of the coil, Fleming's left-hand rule gives forces in opposite directions on each side, forming a couple that rotates the coil. The split-ring commutator reverses the connections to the coil every half turn, so the current in each side reverses direction just as the coil passes the vertical (no-force) position; this keeps the turning force acting in the same rotational sense, allowing continuous rotation. Carbon brushes press against the split-ring commutator to maintain electrical contact between the rotating coil and the fixed external circuit.