Electrical power and the cost of electricity
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 3 worked examples, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Your electricity bill
- Electrical power
- Electrical energy
Read the transcript of the teaching part
Last time
Before we start: last time, in Electrical safety, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Your electricity bill
At the end of each month, your family receives an electricity bill. It does not charge you for current or voltage. It charges you for energy, in units called kilowatt-hours. You can work out the cost of running any appliance with three numbers: its power, the time, and the price of a unit.
Electrical power
Power is the rate of transfer of energy. It is measured in watts. One watt is one joule per second. For an electrical appliance, the power equals the current times the p.d. P equals I V. A 2000 watt kettle on 230 volts takes about 8.7 amperes.
Electrical energy
The electrical energy transferred is the power times the time. E equals P t. Substituting, E equals I V t. Energy in joules, with the time in seconds. Using V equals I R, power can also be written I squared R.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Electrical energy and power · Power · Electrical power and energy · Power · The kilowatt-hour and the cost of electricity.
The whole chapter: Electrical Quantities, Electrical Safety, Energy, Work and Power.
Chapter 4.4: Practical electricity
- Electrical power and the cost of electricity 5 min
- Electrical safety: fuses, earthing, hazards 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.