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KS4 Physics

Mains Electricity

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Mains Electricity

Buying electricity

Contents

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Electricity costs money, which is why every home has an electricity meter.

The meter records how much electricity is used in a house in units of electrical energy.

The units of electrical energy are called kilowatt hours (kWh).

The cost of an electricity bill is calculated from the number of units used.

Buying electricity

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The cost of electricity is the number of units of electrical energy multiplied by the cost per unit:

Example:

How much would 10 units of electricity cost at a price of 9p per unit?

cost = 10 units x 9 p/unit

= 90 p

Cost of electricity

cost = number of units x cost per unit

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Power is measured in kilowatts (kW) and the time is measured in hours (h), so what are the units of electricity measured in?

1 unit of electricity = 1 unit of electrical energy = 1 kilowatt hour (kWh)

Example:

How many units of electricity is 17.6 kWh? 17.6 units

Calculating the units of electricity

The amount of electrical energy (i.e. the amount of electricity) used by an appliance depends on its power and how long the electricity is used for:

electrical energy = power x time

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A kettle uses 45.2 kWh of energy.

If electricity costs 10 p per unit, how much does it cost to use the kettle?

Number of units:number of units of electricity = number of kilowatt hours

= 45.2 units

Cost of electricity:cost = number of units x cost per unit

= 45.2 units x 10 p / unit

= 452 p or £4.52

Buying electricity problem

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An iron that operates at a power of 3 kW for 4 hours uses electricity that costs 8p per unit.

How much does it cost for the electricity used by the iron in that time?

Number of units:number of units of electricity = number of kilowatt hours

= 3 kW x 4 h = 12 kWh = 12 units

Cost of electricity:cost = number of units x cost per unit

= 12 units x 8 p / unit= 96p

Buying electricity problem

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Buying electricity calculations