## What is joule?

Joule is the SI unit of energy or work (energy and work are interconvertible). Its symbol is “J”. It is named after a Scientist James Prescott Joule who worked on the conversion of enegy which led to the law of conservation of energy.

## Equivalent units of joule:

The formula of work / energy is,

W=F.d →1

Where W stands for work, F represents force and d is the distance. We know that the unit of force is newton and in SI system distance is measured in meters so according to this, Joule is equal to N.m

Joule=Newton×meter (N.m) →2

Another equivalent unit for joule can be derived by opening the formula of force in equation 1.

F=ma

W=ma.d

Here m stands for mass and a is the acceleration. Mass is measured in kilograms and unit of acceleration is m/s2 so Joule is also equal to Kgm^2/s^2

Joule=(Kg×m×m)/s^2

Joule=(Kg.m^2)⁄s^2 →3

## Definition of joule:

Joule can be defined in many ways.

- According to the second equation, the amount of work that is done by 1 newton of force in moving an object through a distance of 1 meter is equivalent to 1 joule.
- According to the third equation, the amount of work that is done when 1kg of object is moved 1 meter with an acceleration of 1m/s2 is equal to 1 joule.

## Joule in terms of potential difference:

Let’s see the formula of electric potential difference.

V=W/q →4

V is the potential difference and q stands for charge. The units of potential difference and charge are volt and coulomb (C). This gives us another equivalent unit of joule that is,

Joule=Volt×Coulomb

### Definition of joule:

The above equation has given us another definition of joule. The amount of work done on 1 coulomb of charge when there is potential difference of 1 volt. is equal to 1 joule.

## Joule in terms of power:

P=W/t

P is power here and t is for time. Let’s look in to the units. The SI unit of power is watt and time is measured in seconds so Joule is also equivalent to power x time

Joule=watt×sec

### Definition of joule:

Joule can also be that amount of work which is done in 1 second with power of 1 watt.

### Joule into Kilowatt-hour:

Commercially energy is measured in Kilowatt-hour. 1 kilowatt-hour is equal to 36x10^5 joules.

1 Kilowatt-hour=〖10〗^3×36×〖10〗^2=36×〖10〗^5 Joules

## Conversion of joule into erg:

In CGs (centimeter gram second) system the unit of energy or work is erg.

1 erg=〖10〗^(-7) Joule

## Conversion of joule into Calorie:

Another unit of energy in CGS system is calorie.

1 cal=4.18 Joule

## Conversion of joule into dyn.cm:

Dyne (represented as dyn) is the unit of force in CGS system and in this system distance is measured in cm. According to the formula of energy / work (equation 1) in CGS another unit of energy can be dyn.cm.

1 dyn.cm=1×〖10〗^(-7) Joules

The above equation also shows that the unit dyn.cm is equal to erg.

## Conversion of joule into BTU:

BTU stands for british thermal unit. To convert joule into BTU multiply the value in joule with 1055.

1 BTU=1055 Joule

## Conversion of joule into lb.ft:

In FPS system (foot pound second) the distance is measured in foot (represented as ft) and the unit of force is pound (symbol lb). According to equation 1, in FPS system the unit of energy will be lb.ft.

1 lb.ft=1.356 Joules

## Atomic unit of Energy:

Joule and other units are not convinient to describe the energy of very small particles like electrons and protons. So scientist developed another unit to measure very small energy changes. They called it “Electron Volt”.

### Definition of electron volt:

The amount of energy required by an electron to move in an electric field when the potential difference is of 1 volt.

### Conversion of joule into electron volt:

According to equation 4 (formula of potential difference),

1 ev=1.6×〖10〗^(-19) coulomb ×1 volt

1 ev=1.6×〖10〗^(-19) Joules

**Read also:**

Energy

Watt hour

Energy conservation