Name the device which is used to reverse the direction of current in the coil of a motor .
(a) A current-carrying conductor is placed perpendicularly in a magnetic field. Name the rule which can be used to find the direction of force acting on the conductor.
(b) State two ways to increase the force on a current-carrying conductor in a magnetic field.
(c) Name one device whose working depends on the force exerted on a current-carrying coil placed in a magnetic field.