Question

A house is fitted with $5$ tube lights each of $40\text{W}$. If all of them are lighted for $20$ hours and if the cost of electrical unit is $\text{Rs}.5.00$, the total cost of electricity consumed is

Answer 1

$t=20\text{hr}=20\times 60\times 60\text{sec}$

The power of $5$ tube lights,

$P=5\times 40=200\text{W}$

Total Energy $E=Pt$

$E=200\times 20\times 60\times 60\text{J}$

$=144\times {10}^5\text{J}$

$36\times {10}^5\text{J}\to 1\text{kwh}$

Then $144\times {10}^5\to E^{\prime }=\frac{1}{36\times {10}^5}\times 144\times {10}^5\text{kwh}$

$E^{\prime }=4\text{kwh}$

Each unit is $\text{Rs}.5.00$

Then total amount $=5.00\times 4$

$\begin{array}{c}\text{Rs}.20\end{array}$