Question

SI unit of ‘rate of doing work’ is

• A. J
• B. W
• C. kW
• D. kWh

Answer 1

The correct option is B

W

Explanation for correct option:

(B) W

1. The rate of doing work is called power.
2. Power is given as, $P=\frac{W}{t}$, where, $W$ is work and $t$ is time.
3. Therefore, the unit of power will be, $\frac{unitofwork}{unitoftime}=joules/second(J/s)$
4. $1J/s$ is equivalent to $1watt\left(W\right)$, which is the SI unit for power.

Explanation for incorrect options

(A) J

1. Joule (J) is the SI unit for work and energy.

(C) kW

1. Kilowatt (kW) is a multiple of watt.
2. $1kW=1000W$

(D) kWh

1. Kilowatt-hour is used to measure energy.
2. 1 kWh is equal to the energy consumed by 1 kW (1000 watt) in 1 hour.

Therefore, the SI unit of ‘rate of doing work’ is option (B) watt (W).