Question

(i) Draw a simple labelled diagram of a d.c. electric motor.
(ii) What is the function of the split rings in a d.c. motor?
(iii) State one advantage of a.c. over d.c.

Answer 1

(i) The diagram is as shown in the figure. An electric motor consists of a rectangular coil ABCD of insulated copper wire. The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field. The ends of the coil are connected to the two halves $S_1$ and $S_2$ of a split ring. The inner sides of these halves are insulated and attached to an axle. The external conducting edges of the coil touch two conducting stationary brushes $B_1$ and $B_2$, respectively.

(ii) When the coil rotates, the split parts of ring rotate with it to flow the current in armature coil in such a way that it always keep on rotating in the same direction.

(iii) D.C. can store in battery but A.C. can not be. AC voltages can be readily transformed to higher or lower voltage levels, while it is difficult to do that with DC voltages. Since high voltages are more efficient for sending electricity great distances, AC electricity has an advantage over DC. AC can employ capacitors and inductors in electronic circuitry, allowing for a wide range of applications.