# Electrical energy

Electrical energy and electric power are closely related to each other. Electric energy do the use full work in electric circuit and can be transferred from source to load.
Most of the time electric energy is defined as the product of electric power and time.  But the right way of defining electrical energy is the measure of how much energy is consumed by a electric circuit in given amount of time.

Electrical energy is the energy supplied by the source for maintaining the current in a electrical circuits for a given time. As electric energy supplied by source is the energy loss in circuits
Therefore electrical energy is the energy that is loss by a moving charge particles to preform some useful work in electric circuit.

## Difference between electric power and electric energy

The most basic difference between electrical energy and Electrical power is
– electrical energy is measured of how much electrical energy is consumed by a electrical circuits.

– electrical power is the measures of how fast electrical energy is consumed by a electrical circuits.

Electric energy can be transformed into another form of energy. In a electric circuit, charge particles are used to transfer energy from source to load.
As electric power is the rate at which charge is transferred from source to load. Let charge ‘q’ move from one terminal of battery to another terminal. It losses electric potential energy of ‘qV’ Joule. Therefore energy consumed is equal to ‘qV’.
Energy consume = qV = (It)V
Energy consume = VIt
Therefore,
Energy consume = P × t

Electric energy is the product of electric power and time.

## Unit of electrical energy

Electrical energy = Power × time
E = watt × sec
E = (joule/sec) × sec
Energy = joule

Therefore the unit of energy is ‘Joule’.

In electrical circuit electrical energy is generally measured in watt-hours or kilowatt-hours. Electrical energy is measured in Kilowatt hours because it is a much battery unit for large amount of energy.

1 kWh is defined as the energy consumed by electric devices and circuits 1 kW during 1 hour.

For example, let us consider a electric heater of 1 kW connected across its rated supply voltage. Let heater is ON for 1 hours. Then energy consumed by heater is said be one unit or 1 kWh.

1 kWh  =  1kW × 1 h
1 kWh  =  1000W × 3600 sec
1 kWh  =  3.6 × 10^6 ( W×sec )
1 kWh  =  3.6 × 10^6 joule

1 kWh of energy consuming is said to be 1 unit

Therefore,
One unit = 1 kWh  =  3.6 × 10^6 joule

## Joule Law of Heating

When a electric current flow through a resistance, it produce heat which is expressed in Joule’.  Joule law gives a relationship which is used to calculate heat produce by current when it flow through a resistance for a given amount of time.

When a current of I ampere flow though a resistance of R ohms for t second then heat generated or energy expended in Joule is given as
H  =  I2 R t    joules

This expression is known is Joule Law, which state that the amount of heat produced in an electric current is
(1) directly proportional to the square of the current i.e. H
I2
(2) directly proportional to the resistance of the circuit i.e. H
R
(3) directly proportional to the time of current flow i.e. H
t

Heat produce in cals,
H = I2 R t / 4.2 = 0.24 I2 R t  cals.

Example: An electric heater having a resistance of 100 ohm is connected across a rated supply voltage of 220 Volt. Calculate the energy consume by heater when it is ON for 3 hours.

First step is collect all the data given in questions:
Resistance of heater, R = 100 ohm
Supply voltage, V = 220 V
Therefore,
Electrical Power = VI = I2R = V2/R = (220 × 220)/100 = 484 watt

As we know that energy consume = Power × time
Therefore, Energy consume in 3 Hours is
E = 484 watt × 3 hours
E = 1452 Wh
E = 1.45 kWh
E = 1.45 unit

Electric energy consume by heater is 1.45 unit in 3 hour.