Electricity & Megnetism

electrical energy:definition,formula,unit,examples and uses

Electrical energy definition

“Electrical energy is produced by moving electric charges commonly through a wire.”When charge moves from a higher electric potential to a lower potential,it delivers electric current.Thus,the process ,during which charges continuously move from a higher potential to a lower potential,becomes a continuous source of electrical.E.

Examples of electrical energy

Turbine runs generator to produce electrical energy when water falls on it from higher gravitational potential to a lower gravitational potential.Lightning,electrical charges moving through a wire,batteries in use,electricity stored in capacitors,door bells,audio speakers etc..are few examples.

Unit of electrical energy is joule (J).It is commonly consumed in very large quantity for the measurement of which joule is a very small unit.Hence,a very large unit of electric energy is needed which is called kilowatt hour.

Kilowatt-hour definition

“The amount of energy delivered by a power of one kilowatt in one hour is called kilowatt hour.”When you pay your electric bill you are charged on the basis of the amount of energy you use,not the power,because power companies deal in huge amount of energy,the most practical unit is the kilowatt hour, you use a kilowatt hour of energy when you used one thousand watts of power for one hour.For example ,a 100 W light bulb burning for 10 h uses 1KWh of energy.

Relation of kWh with MJ:

One kilowatt-hour 1kWh=1000W×1 hour


= 3600000J


Formula to find energy in KWh:

The energy in kilowatt-hour can be obtained by the following formula:

The amount of energy in kWh=watt×times of use in hours/1000

Unit followed by electric meter in our houses:

The electric meter installed in our houses measures the consumption of electric energy in units of kilowatt-hour according to which we pay our electricity bills.

Calculation of electric bills:

If the cost of one kilowatt-hour  i.e one unit is known,we can calculate the amount of electricity bill by following formula:

Cost of electricity=number of units consumed×cost of one unit

            Cost of electricity=watt×times of use in hours/1000 ×cost of one unit

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