Which of the following is NOT a unit of energy?
A. Watt
B. eV
C. Kilowatt hour
D. Joule
E. Calorie

Answer
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Hint: We will study about definition and different forms of energy along with all the units of measurement of energy. We will then consider all the given options to identify the term which is not the unit of energy.

Complete step by step answer:
Energy is referred to the quantitative property that must be transferred to a body in order to perform work on the object. This work done can also be transferred in the form of heat. We can also say that energy is the capacity of doing work. It may exist in various forms such as kinetic, potential, thermal, chemical, electrical, nuclear etc. Energy is the ability to do work. It means how things change and move. It is present everywhere around us and takes all sorts of forms.

Different forms of energy are:
1. Sound energy – It is produced when an object is made to vibrate.
2. Chemical energy – It is actually a form of potential energy.
3. Radiant energy – It is a combination of heat and light energy.
4. Electrical energy – It is the energy produced by electrons moving through a substance.
5. Atomic energy – It is produced when an atom is split.
6. Mechanical energy – It is moving energy. All moving objects produce mechanical energy.

Different units of energy:
1. SI unit – Joule
2. CGS unit – erg
3. MKS unit – Joule
4. British thermal unit (BTU)
5. Kilowatt-hour (KWh)
6. Calorie
7. Electronvolts (eV)
$\begin{align}
  & 1J=1Kgm{{s}^{-2}} \\
 & 1\text{ erg}={{10}^{-7}}J \\
\end{align}$
Joule, Calorie, eV, Kilowatt hour; all are the units of energy. Watt is not the unit of energy. It is the SI unit of electric power. Power is defined as the rate of doing work.
$\text{Power = }\dfrac{\text{Energy}}{\text{time}}$
The SI unit of power is Watt. 1 Watt is equal to 1 Joule per second.
$\text{1Watt = 1}\dfrac{\text{Joule }}{\text{second}}$
Hence, the correct option is A.

Note: Energy is the measure of total amount of work done, while Power is how fast you do the work. In other words, power is energy per unit time. Energy and power exist in various forms and have different units of measurement. The SI unit of energy is Joule and the SI unit of power is Watt. 1 Watt is equal to 1 Joule per second.