PHYSICS · Multi-part · CBSE · Physics · Magnetic Effects of Electric Current · Magnetic Effects of Electric Current
Problem
A simple d.c. motor consists of a single rectangular coil ABCD mounted on an axle between the poles of a permanent magnet.
(a) Draw a neat, labelled diagram of this motor showing the coil, magnetic field, split-ring commutator and brushes.
(b) When the coil is in the horizontal position, identify the directions of the forces acting on arms AB and CD and state the direction of rotation of the coil as viewed from side A.
(c) Explain why the coil continues to rotate in the same direction even though the current in each arm reverses every half turn.
(d) When the coil becomes vertical, the turning moment is zero. Describe how the motor crosses this position and continues to run.