DC Motors

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When a current flows through a wire in a magnetic field the wire experiences a force in a direction given by Fleming\'s Left Hand Rule. If we wind the wire into a coil, the force will be in the opposite sense on opposite sides of the coil and a turning force will result. We can make an electric motor by connecting a source of direct current to a slip ring, and connecting the ends of the coil a rotating commutator and the external circuit to a pair of brushes.
The direction of the force on each arm of the coil in the magnetic field will change direction - from up to down and vice versa - each time the coil reaches the vertical, and the coil will experience a tuning force in the same sense.
The force on each arm of the coil is maximum when the coil is horizontal and minimum when the coil is vertical.