Question

An electric heater of resistance $8\Omega$ draws a current of $15\text{A}$ from the service mains operated for $2\text{h}$. What is the cost of the energy to operate it for $30$ days at Rs $3.00$ per $\text{kWh}$?

• A. Rs. $108$
• B. Rs. $324$
• C. Rs. $360$
• D. Rs. $420$

Answer 1

The correct option is B Rs. $324$

Given:
Resistance, $R=8\Omega$
Current drawn, $i=15\text{A}$
Time duration, $=2\text{h}$ per day.
Cost of operating, Rs. $3$ per $\text{kWh}$

The energy $E$ consumed by the heater in 1 day would be:

$E=i^{2}Rt={15}^2\times 8\times 2$
or $E=3600\text{Wh}=3.6\text{kWh}$

The total energy $H$ consumed by the heater in $30$ days would be:
$H=3.6\times 30\text{kWh}=108\text{kWh}$

Cost of operating at the rate of Rs. $3/\text{kWh}=3\times 108$
$⟹$ Rs. $324/-$