Question

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

• A. $11$
• B. $13$
• C. $15$
• D. $17$

Answer 1

The correct option is B $13$

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