$(a)$ Draw a schematic labelled diagram of a domestic wiring circuit which includes $(i)$ a main fuse,$(ii)$ a power meter,$(iii)$ one light point,and $(iv)$ a power plug.
$(b)$ Why is it necessary to connect an earth wire to electric appliances having metallic covers?

(N/A) The schematic diagram of a domestic wiring circuit is provided in the image.
$(b)$ It is necessary to connect an earth wire to electrical appliances having metallic covers to protect us from the harmful effects of electric shock. In the event of any leakage of current or any other electrical defect,the earth wire provides a low-resistance path to the ground,thereby carrying the excess current to the earth and preventing the user from receiving a shock.