New
New
Year 11
Edexcel
Higher
Power of an appliance or electric circuit
I can describe how the power of an appliance or electric circuit depends on current and potential difference.
New
New
Year 11
Edexcel
Higher
Power of an appliance or electric circuit
I can describe how the power of an appliance or electric circuit depends on current and potential difference.
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Lesson details
Key learning points
- Power is the amount of energy transferred per second and is measured in watts (W).
- Power can be calculated using the equation: power = current × potential difference (P = I V).
- At a constant p.d., a larger electric current transfers energy more quickly than a smaller current.
- Domestic appliances plugged into the mains supply in the UK have a p.d. of 230 V across them.
- The fuse with the smallest rating for the required current (calculated using the equation: P = I² R) should be used.
Keywords
Power - the amount of energy transferred each second
Watts (W) - the unit of power; equal to the number of joules of energy transferred each second
Kilowatts (kW) - a unit of power; 1 kilowatt is equal to 1000 watts
Fuse - a thin wire that melts when a dangerously large current flows through it
Common misconception
Pupils often use the terms power and energy interchangeably.
Use concrete examples to show pupils that a greater power transfers energy more quickly.
Comparing the heating effect of different power settings on a microwave oven is a good way to illustrate that power is proportional to the amount of energy transferred per second.
Teacher tip
Licence
This content is © Oak National Academy Limited (2025), licensed on
Open Government Licence version 3.0
except where otherwise stated. See Oak's terms & conditions (Collection 2).Lesson video
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Starter quiz
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6 Questions
Q1.
Which of the following are ways of writing the definition of power?
amount of energy used up per second
time taken to use up one joule of energy
Q2.
A mains circuit includes a fuse. Which of the following makes a fuse ‘blow’?
a circuit resistance that is too high
a room temperature that is too high
Q3.
What is the potential difference across the resistor in the circuit shown?
0.75 V
1.0 V
2.5 V
3.0 V
Q4.
What is the missing current in the circuit shown?
1.5 A
3.5 A
5.0 A
Q5.
A cell is connected to a lamp and a current flows. What happens to the current through the cell if another lamp is added in parallel with the first lamp?
It stays the same.
It decreases.
Q6.
An ammeter shows that the current through a resistor is 0.40 A and a voltmeter shows that the p.d. across it is 1.5 V. A pupil calculates the resistance. Which of these answers should they give?
3 Ω
4 Ω
3.7 Ω
3.75 Ω
Exit quiz
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6 Questions
Q1.
A lamp has power of 7 W. Which of the following explains what this means?
The lamp transfers 1 J in 7 s.
The lamp transfers 1 W in 7 s.
The lamp transfers 7 W in 1 s.
Q2.
When an iron is working correctly, the current through it varies between 1.6 A and 3.3 A. Which of the following fuse sizes should be used in the plug of this iron?
3 A
13 A
Q3.
Which of the following could cause a circuit breaker to switch off a circuit?
no appliances being used
too many appliances being connected in series
Q4.
The current through a lamp is 1.5 A and the p.d. across it is 12 V. The power of the lamp is W.
Q5.
What is the current through a 600 W lawnmower that is plugged into the mains?
0.38 A
4.7 A
6.0 A
Q6.
A 1300 W iron and a 1000 W hairdryer are plugged into a mains circuit, in parallel. What is the current through a circuit breaker in the consumer unit?
0.10 A
0.77 A
1.3 A
5.3 A