Question

An electric blub of $60\mathrm{W}$ is used for $6\mathrm{h}$ per day. Calculate the units of energy consumed in one day by the bulb.

Answer 1

Step 1: Given data:

Power of the bulb is $\mathrm{P}=60\mathrm{W}=60\mathrm{J}/\mathrm{s}$

Total number of hours the bulb is used in $1\mathrm{day}\mathrm{is}\mathrm{t}=6\mathrm{hours}=(6\mathrm{hours})\mathrm{x}(3600\mathrm{s}/\mathrm{hour})=21600\mathrm{s}$

Step -2 Finding the energy consumed:

$1\mathrm{W}$ signifies that $1\mathrm{J}$ of energy is consumed in $1\mathrm{s}$.

So, a $60\mathrm{W}$ bulb will consume$60\mathrm{J}$ of energy in $1\mathrm{s}.$

Mathematically we can see that $\mathrm{Energy}=\mathrm{power}\mathrm{x}\mathrm{time},or\mathrm{E}=\mathrm{p}\mathrm{x}\mathrm{t}$ where $\mathrm{E}$ is the total energy consumed.

The magnitude of energy is $\mathrm{E}=(60\mathrm{J}/\mathrm{s})\mathrm{x}(21600\mathrm{s})=1296000\mathrm{J}=1.296\mathrm{x}{10}^6\mathrm{J}$

Step -3 Finding the energy in units:

Since, ⁣$1\mathrm{unit}=1\mathrm{kWh}=3.6\mathrm{x}{10}^6\mathrm{J}$

Then, energy in units = $\frac{1.296\mathrm{x}{10}^6\mathrm{J}}{3.6\mathrm{x}{10}^6\mathrm{J}}=0.36\mathrm{units}$

Thus, $0.36\mathrm{units}$ of energy is consumed in one day by the bulb.