Question

Capacity of doing work is called ……………………. (Power, energy)

Answer 1

Hint: In this question use the basic definition of energy that is energy itself is defined as the capacity to do work. In this we can also think of some real life examples that will help differentiating between the power and the energy.

Complete step-by-step answer:
Consider an example of an electrical equipment, say a ceiling fan of 250 watts rating.
So this electric fan consumes 250 watts from the supply.
This is called the power (P) of an equipment measured in watts or in kilowatts.
Now let us assume that this fan runs 10 hours in a day.

So the energy (E) consumed by the fan is the product of power of the fan and the time (t) of running.
$ \Rightarrow E = P \times t$
And it is measured in Joules (J).
Now we have to find out what is the capacity of doing work.
So when we run a ceiling fan it gives us air so it is done according to its capacity.
Now we run a fan for about 10 hours in a day.
So the work done by the fan is the energy consumed by the fan in that interval of time.
$ \Rightarrow E = 250\left( {10} \right) = 2500$ Watt-hour.
Now as we know 1 hour = 60 sec, and 1kw = 1000 watt.
Therefore, 2500 watts = 2.5 Kw.
$ \Rightarrow E = 2.5 \times 60 = 150$ Kw-sec or joules (J).
So capacity of doing work is nothing but the energy or we can say that the energy is defined as the capacity of doing work.
So this is the required answer.

Note: The more physical interpretation of power is that it is defined as how fast a wok can be done. Power can also be termed as the energy per unit time. S.I unit of power is watt however that of energy is joule. The ability of an engine to do work is its power that is why we generally come across notations like this engine is of 700 horsepower.