[Physics Class Notes] on Unit of Energy Pdf for Exam

In simple terms, energy can be thought of as the ability to do work. It can be kinetic, potential, electrical, chemical, nuclear, thermal, and many other forms, as well. Renewable energy and non-renewable energy are two types of energy.

What is the Unit of Energy?

In physics, we encounter various quantities having varying attributes, and describing them becomes difficult as we talk about the terms like energy, time, work, or any physical quantity that needs to have a standard measure to distinguish. In physics, the units determine the standard measure of these quantities. Such as if I say my aunt is 36 kg and she lives 1200 km from my city. Here, kg (for weight) and km (for distance)  are the units to describe these physical quantities. Other examples are Kelvin for temperature; etc.

Because energy is defined in terms of work, the SI unit of energy is the joule (J), which was named after James Prescott Joule and his investigations on the mechanical equivalent of heat.

In more basic terms, 1 joule equals 1-newton meter and, in terms of SI base units.

[1J = 1kg(frac{m}{s})^{2} = 1(frac{kgm^{2}}{s^{2}})]

The unit of energy is the same as that of work (As work and energy are the two sides of the same coin).

The SI Unit of Potential Energy

‘Potential energy’ is how much power you have to do something. The more work you do, the more energy you need.

The potential energy is the energy stored in the matter. Therefore, the SI unit of potential energy is the same as the SI unit of all energies are given by,

[1 J =  1 kg m^{-2} s^{-2}] where the potential energy due to height is described as,

 P.E. =  mgh whose MKS unit is also kg [m^{2} s^{-2} = 1 Joule].

CGS Unit of Energy

An erg is a measure of energy that is equal to [10^{-7}~J]. An erg is the amount of work performed by a single dyne over a one-centimeter distance.

• The CGS stands for centimeter-gram-second.

• The CGS unit of energy is erg equivalent to [1 g cm^{2} s^{- 2}].

• Ergs are a lot smaller than Joules, equivalent to  [10^{-7}~J].

CGS Unit of Power

Power is defined as the rate of doing work given by,

Power = Work/time

The CGS unit of power is erg per second. 

CGS Unit of Work

• The CGS unit of work is Erg where 1 erg = 1 gm cm square/ second square.

• The word erg is derived from the Greek word ergon (ἔργον) which means ‘work’ or ‘task’.

• One erg is also defined as the work done by a force of 1 dyne at a one-centimeter distance.

Unit of Energy in MKS System

The MKS stands for meter-kilogram-second.

1 Joule is equivalent to one Newton-meter (N-m) where 1 J is the amount of work done by a newton of force to a distance of 1 meter.

Where [1 J = kg (m/s)^{2}] = 1 Watt-second = 1 kg [m^{2} s^{- 2}].

So MKS unit of energy is kg [m^{2} s^{- 2}].

A force does the work to accelerate a body of mass 1 kg at the rate of [1 ms^{-2}].

Unit of Energy – Electricity

The kilowatt-hour (kWh) is a measure of electrical energy that is commonly used in utility bills; one kilowatt-hour is equal to 3.6 megajoules.

The SI Unit of Electrical Energy

The movement of charged particles inside the wire produces electricity. Electrical energy is the form of energy resulting from the flow of electrical charge is called electrical energy.

• The SI unit of electrical energy is Joule symbolized as J.

• 1 Joule is equal to the energy transferred (or work done) when applying a force of one newton through a distance of one meter (1 newton-meter or N-m), 

• It is also defined as the work done in passing an electric current of one ampere through a resistance of one ohm for one second.