The figure shows a horse-shoe magnet placed along geographics west-east and a horizontal conductor carrying current along geographic south-north. Find the direction of magnetic force on the conductor.

The figure shows a rectangular current-carrying coil $PQRS$ placed between the poles of a horse-shoe magnet producing field $B$. Write magnitude and direction of the force on each of the parts$PR$,$RS$, $SQ$ and  $QP$ of the coil.

Describe the principle and working of a d.c. motor. Label each part of this motor and state three factors that increase the speed the motor.