Question

Calculate the electric bill at the end of a month of $30$ days at $Rs.2.00$ per unit if $6$ lamps of $40watt$ each burn for $8$ hours per day, an electric iron of $1kW$ is used for $2$ hours per day and $4$ fans of $50watt$ each are used for $10$ hours per day.

Answer 1

Given:

Rate of one unit $=Rs.2.00/unit$

Also, $1unit=1kWh$

So let us calculate the total energy consumed by all the appliances.

Energy consumed by an appliance in kWh $=Power\left(inkW\right)\times time\left(inhours\right)$

Power of a lamp $P_1=40W=40\times {10}^{-3}kW$

Time for which it is operated per day $t_1=8hrs$

Energy consumed by 6 lamps per day $E_1=6\times P_1\times t_1$

$=6\times (40\times {10}^{-3})\times 8$

$=1.92kWh$

Power of an electric iron $P_2=1kW$

Time for which it is operated per day $t_2=2hrs$

Energy consumed by the iron per day $E_2=P_2\times t_2$

$=1\times 2$

$=2kWh$

Power of a fan $P_3=50W=50\times {10}^{-3}kW$

Time for which it is operated per day $t_3=10hrs$

Energy consumed by 4 fans per day $E_3=4\times P_3\times t_3$

$=4\times (50\times {10}^{-3})\times 10$

$=2kWh$

Total energy consumed per day $E_{total}=E_1+E_2+E_3$

$=1.92+2+2=5.92kWh$

Total energy consumed per month $E_{month}=30\times E_{total}$

$=30\times 5.92$

$=177.60kWh$ or $177.60units$

Bill for one month $=Rate/unit\times units=\left(Rs.2.00/unit\right)\times \left(177.60units\right)$

$=Rs.355.20$

So the electric bill at the end of a month will be $Rs.355.20$