Question

(a) Write two points of difference between electric energy and electric power (b) Out of $60\mathrm{w}$ and $40\mathrm{w}$ lamps which one has higher electrical resistance when in use?

Answer 1

(a) Difference between electric energy and electric power.

	Electric energy	Electric power
1	The work done or energy supplied by the source in maintaining the flow of electric current is called electrical energy. It appears in the form of heat given by $$\begin{gathered} \mathrm{H}=\mathrm{VIt} \\ =\frac{V^2\mathrm{t}}{R} \\ ={\mathrm{I}}^2\mathrm{RT} \end{gathered}$$	The time rate at which electric energy is consumed or dissipated by an electrical device is called electric power and is given by $$\begin{gathered} \mathrm{P}=\mathrm{VI} \\ =\frac{V^2}{R} \\ ={\mathrm{I}}^2\mathrm{R} \end{gathered}$$
2	It is equal to the product of power and time $\mathrm{E}=\mathrm{P}\times \mathrm{t}$	It is equal to the rate of doing work by an energy source. $\mathrm{P}=\frac{\mathrm{W}}{\mathrm{t}}$
3	Its SI unit is the joule $\left(\mathrm{J}\right)$.	Its SI unit is a watt $\left(\mathrm{W}\right)$.

(b) To find the lamps which one has higher electrical resistance when in use

For the same applied voltage,
$\begin{array}{r}\mathrm{P}=\frac{{\mathrm{V}}^2}{\mathrm{R}}\\ \mathrm{P}\propto \frac{1}{\mathrm{R}}\end{array}$
The less the power of an electrical device, the higher its electrical resistance. So $40\mathrm{W}$ lamp will have higher resistance.