(a) Whenever there is a change in the magnetic flux linked with a circuit, an e.m.f. is induced, the strength of which is proportional to the rate of the change of the flux linked with the circuit. The direction of the induced current is always such as to oppose the change producing it.

As coil is rotating in the magnetic field, an e.m.f which is due to the changing flux induces between its terminals. The e.m.f. varies from maximum when the coil is horizontal to minimum when the coil is vertical at which position connections between brushes and terminals of coil are changed by commutator. This ensures that current continues to flow in the same direction.
(c) – By increasing the number of turns – Winding the coil on the soft iron core – Increasing the strength of the magnet – turning the coil faster.