Question

The maximum number of 40 W tube-lights connected in a parallel which can safely be run from a 240 V supply with a 5 A fuse is:

(a) 5
(b) 15
(c) 20
(d) 30

Answer 1

(d) 30

Let n be the number of tube-lights that can be used safely.
It is given that:
Power of one tube-light = 40 W
Therefore, Power of n tube-lights, P = 40 $\times$ n watts
Potential difference, V = 240 volts
Current, I = 5 amperes
We know that:
P = V $\times$ I
or, 40 $\times$ n = 240 $\times$ 5
or, n = 30
Thus, the maximum number of tube-lights that can safely be run is 30.