Question

Which of the following is the biggest unit of energy?

• A. Joule
• B. Kilowatt hour
• C. Erg
• D. Electron volt

Answer 1

Answer: (B)

Since, we know that SI unit of energy is represented by Joule. Hence, let us convert all the different units in the form of Joules.

Option A-

1 Joule= $1Joule=\left[kg\right]{\left[\frac{m}{s}\right]}^2$

Option B-

$kWh=1000W\times 3600s=3600000W\times s$

As we know that 1 Ws = 1 Joule

So 1 kWh= 3600000 Joules

Option C-

$1Joule=\left[kg\right]{\left[\frac{m}{s}\right]}^2=\left[1000gm\right]\left[\frac{100cm}{1s}\right]\left[\frac{100cm}{1s}\right]S0,1Joule={10}^{7}gm\frac{{cm}^2}{s^2}={10}^{7}ergSo,1erg={10}^{-7}Joule$

Option D-

Electron Volt is the unit of energy in terms of change in energy for one electron in the potential difference of one volt. So, mathematically it is-

$1ev=Chargeofoneelectron\times 1Volt=1.6\times {10}^{-19}Coloumb\times 1\frac{Joule}{Coloumb}So,1ev==1.6\times {10}^{-19}Joule$

Hence, Option B is the largest unit of energy and hence it is practically used in everyday life of electric consumption.