Question

What is the commercial unit of energy? What is the SI unit of electrical energy? A body does 20 joules of work in 5 seconds. What is its power? [4 Marks]

Answer 1

The commercial unit of energy is kilowatt- hour (kWh) [1 Mark]

The SI unit of electrical energy is joule (J). [1 Mark]

Power is calculated by using the formula: [2 Marks]

Power $=\frac{Workdone}{Timetaken}$

Here,
Work done = 20 J
Time taken = 5 s
Thus,
Power $=\frac{20J}{5s}$$=4J/s$
Now, since 1 J/s = 1 W;
Power = 4 W