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Electrical energy and cost
Beginner
Bills use kilowatt-hours.
Domestic meters record kWh. Cost = kW × hours × tariff.
A 100 W TV for 5 h is 0.5 kWh.
Convert W to kW first.
In more detail
Electrical energy is measured in kilowatt hours, equal to the power in kilowatts multiplied by the hours of use. The cost of electricity is this energy times the price per unit.
Real-world uses
- Households estimate the cost of running appliances from their power ratings.
- Businesses compare energy-efficient equipment by annual cost.
- Households pay for the energy their appliances use, measured in kilowatt-hours, which is the power multiplied by the time.
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Frequently asked questions
How much does a 100 W bulb cost to run for 10 hours?
It uses 1 kWh, so the cost is the price per kWh times one.
Is energy the same as power?
No. Power is the rate of energy transfer, while energy is the total amount.
How do I work out the cost of running a light?
Multiply the power in kilowatts by the hours of use, then by the price of one kilowatt-hour.
Related topics in Current Electricity & Circuits
Colour code of resistors · Electric power · Heating effect of current · EMF and internal resistance · Cells in series and parallel · Kirchhoff's current law