Question

Fig . shows the essent ial features of a battery operated bell. The hammer strikes the gong when the swi tch is closed . State and explain the effect of using the following material successively to form the core.

(a) Plastic
(b) Steel
(c) Copper

Answer 1

(a) Plastic being non-magnetic cannot be used as a material for core. It shall not intensify the formed magnetic field.
(b) Steel has high retentivity. Hence, after prolonged use even when the switch is off, it may retain some magnetic property and attract the armature.
(c) Using copper as a material for core will introduce eddy currents in the core and thus, interfere with the working of the bell.