Question

Electric supply of a house is through a 15 A fuse. When a 2000 W heater is used in this house, how many 100 W bulbs can be used simultaneously ? The supply is at 220 V, and the heater and the bulbs are rated for 220 V.

• A. 12
• B. 13
• C. 14
• D. 15

Answer 1

The correct option is B 13

The current drawn by the 2000 W heater is
$I=\frac{P}{V}=\frac{2000W}{220V}=\frac{100}{11}A$
The maximum current the bulbs can draw is
$15A-\frac{100}{11}A=\frac{65}{11}A$
Each bulb will take a current
$I=\frac{P}{V}=\frac{100W}{220V}=\frac{5}{11}A.$
The number of bulbs that can be used is $\frac{Maximumcurrentthebulbscandraw}{Currentdrawnbyeachbulb}$
$\frac{\frac{65}{11}A}{\frac{5}{11}A}=13$.