Question

The maximum number of 40 W bulbs connected in parallel which can be lighted safely using a 240 V supply with a 5A fuse is.

• A. 30
• B. 45
• C. 8
• D. 44

Answer 1

The correct option is A 30

Answer is A.
Fuses are safety devices that are to be built into our electrical system. If there were no fuses and we operated too many appliances on a single circuit, the cable carrying the power for that circuit would get extremely hot, short circuit, and possibly start a fire. To prevent electrical overloads, fuses are designed to trip or blow, stopping the flow of current to the overloaded cable.
The fuse must always be connected to the mains and it must be of correct value. For example, a 15-ampere fuse should trip when the current through it exceeds 15 amperes. A 20-ampere fuse should blow when the current through it exceeds 20 amps.
In this case, the bulb is 40 W and the voltage is 240 V.
That is, P = VI, I = P/V = 40/240 = 0.16 A.
The current drawn from a single 40 W bulb is 0.16 A.
Therefore, with a fuse of 5 A, let the number of bulbs that can be used is given as follows.
I * x = 5 A, That is, x = 5/0.16 = 31.
So, 30 bulbs can burn with a 5 A fuse.