Question

(a) When does a fuse cut off current ? How does it do it ?

(b) What is the maximum number of 60 W bulbs that can be run from the mains supply of 220 volts if you do not want to overload a 5 A fuse ?

Answer 1

(a)A fuse cuts off current when the current exceeds a safe value (due to short circuit or overloading). When the current becomes too large , it heats the fuse wire too much. Since the melting point of fuse wire is low, it melts and breaks the circuit. Thus, current in the circuit is cut off.

(b)Let max number of bulbs be y
Then power of y bulbs = 60y W
As we know, P = VI
So max power = 220 x 5 = 1100 W

60 y = 1100
y = 18.33
So 18 bulbs can be run from the mains supply of 220 volts if I do not want to overload a 5 A fuse.