Question

How much energy in $kilowatt-hour$ is consumed in operating ten 50watt bulbs for 10hours per day in a month (30days)?
(A) $1500$
(B) $15000$
(C) $15$
(D) $150$

Answer 1

Hint: From the question we are asked to find the energy consumed in $\text{kilowatt hour}$. So we use the expression for energy which gives us the relation between energy consumed by a bulb, the time period of operation, and the power of the bulb.
Formula used:
$E = P \times T$. Energy is equal to power times time.

Complete step by step answer:
Let $N, P, E, T$ be the number of bulbs, the power consumed, energy, time in hours. But it is given in months in the question so we convert the time to hours as the units for power is $\text{kilowatt hour}$.
Given,
$ N = 10 $
$ P = 50watt$
$T = 30 \times 10hrs $
$ \Rightarrow T = 300hrs$
The bulb is being used for ten hours every day for a month, so we multiply $30 \times 10$
Now using the formula for finding energy,
$E = P \times T $
$\Rightarrow E = 50 \times 300 $
$\Rightarrow E = 15000watt $
This is per single bulb to find the energy consumed by ten bulbs,
$\Rightarrow E = 10 \times 15000 $
$\Rightarrow E = 150000{\text{watt hour}} $
Converting it into kilowatt-hour we get,
$\Rightarrow E = 150000 \times {10^{ - 3}} $
$\Rightarrow E = 150kwatt.hr $

Hence, the correct answer is option (D).

Additional information:
An electricity meter, electric meter, electrical meter, or energy meter is a device that measures the amount of electric energy consumed by a residence, a business, or an electrically powered device. The unit for electricity meters is also kilowatt.hr. $\text{kilowatt hour}$ is defined as the energy consumed by the power consumption of 1kW for 1 hour.

Note: This question is a simple straight forward question, although the only place a person can go wrong is while converting watt hour to $\text{kilowatt hour}$. Also to convert the time to hours as in the question it is given ten hours per day for thirty days, so we calculate the total hours used by the bulbs.