Electrical power and the electricity bill
Run household appliances for different hours each day, read the meter, and work out the monthly units and the cost.
Core concept
Energy used (kWh) = power (kW) × time (h); the bill depends on both how powerful an appliance is and how long it runs
Topic: Electricity
Power is how fast an appliance uses electrical energy: What is needed to make things move, heat up, light up or grow. All key words, measured in watts (W); 1000 W = 1 kW. Its power is printed on its label. The energy used depends on the power and the time it runs: energy (kWh) = power (kW) × time (hours). One kilowatt-hour is one "unit" on the electricity bill. The current: The flow of electricity through a wire, measured in amperes (A). All key words an appliance draws from the 230 V mains is I = P ÷ V. Powerful heating appliances like kettles and irons use a lot of energy even in a short time, while LED bulbs use very little.
What you will learn
- Calculate energy used in kWh from power and time.
- Calculate the monthly cost of running an appliance.
- Compare the energy use of different appliances and suggest ways to save energy.
Before you start
- Know that power is measured in watts.
Materials
- Labels showing the power of household appliances
Equipment
- Electricity meter (or a plug-in energy meter)
Procedure
- Run the LED bulb for 4 hours a day and record the monthly units and cost.
- Replace it with the old filament bulb for 4 hours a day and compare.
- Run the electric kettle for half an hour a day and record.
How this simulation is simplified
- Mains voltage is 230 V and a month has 30 days.
- A simple flat rate of Rs 10 per unit is used; real NEA tariffs depend on how many units you use.