Question

Which of the following is different from others
A. Joule
B. kilowatt.hour
C. Erg
D. Watt

Answer 1

There are different systems to define units of certain measurement.The systems are MKS (metre kg second), CGS(centimeter gram second) and British system.The internationally accepted system for weight and measures is SI system which is MKS system. The different systems may have different conversion factors to interconvert the values obtained in the solution.

Complete step by step answer:
In the question we are asked to find out the difference between the four options. If said in a simple sense the three of the four options will have the same properties and one will differ in it. We have given four options which we will see one by one,
Joule: Joule is the unit of energy or work. It is named after a scientist. This unit is the standard unit for which is internationally accepted. This will be a unit in the MKS system as $k{g^2}{m^2}{s^{ - 2}}$.

kWh: This unit we will generally hear in the conversations of electrical bills. This unit is used to count the usage of electricity and then ask the customer to pay for it. The price per kWh is decided by the government. The number of units of electricity consumed multiplied by this price is the total electricity bill of that person.
Watt can also be written as $J{s^{ - 1}}$ and one hour =3600s
$1kWh = 1000 \times 1J{s^{ - 1}} \times 3600s \\\ \Rightarrow 1kWh = 3.6 \times {10^6}J$
Which again came out to be the unit of energy $J$.

Erg: Erg is the unit used for energy in the CGS system. As we have stated earlier, energy can be written in MKS units as $k{g^2}{m^2}{s^{ - 2}}$. We can convert this into CGS system as
k{g^2}{m^2}{s^{ - 2}} = 1000 \times {100^2}{g^2}c{m^2}{s^{ - 2}} \\\ \Rightarrow k{g^2}{m^2}{s^{ - 2}} = {10^7}{g^2}c{m^2}{s^{ - 2}} \\\ \therefore 1J = {10^7}erg \\\
Watt this is the only unit which is not used for energy and is a unit of power. Others can be converted to Joule but the unit of power is Joule per second.

Hence, option D is the correct option.

Note: The system of measurement is based on two basic principles. The basic unit is to be defined on the basis of various physical quantities which are also known as independent quantities. The conversions of these units from one into the other systems must be defined for easy operation and conversions.