10 GCSE Physics questions about the smart meter that get harder as you go, from Foundation to Higher, each with a full worked solution. A smart meter measures how much electrical energy a home uses, in kilowatt-hours, and sends the readings to the energy supplier. Its in-home display shows the power being used right now and how much it is costing.
Course: Combined Science + Separate Physics | Tier: Foundation + Higher | Topics: Energy, Electricity
📌 KEY DEFINITIONS – learn them word for word
Power: the rate at which energy is transferred. 1 watt = 1 joule per second.
Kilowatt-hour (kWh): the energy transferred by a 1 kW appliance in 1 hour. 1 kWh = 3.6 × 106 J.
Mains electricity: in the UK, an alternating current (a.c.) supply with a frequency of 50 Hz and a potential difference of about 230 V.
Equations you’ll use
| Quantity | Symbol | Unit |
|---|---|---|
| power | P | watts (W) or kilowatts (kW) |
| energy transferred | E | joules (J) or kilowatt-hours (kWh) |
| time | t | seconds (s) or hours (h) |
| potential difference | V | volts (V) |
| current | I | amps (A) |
Use FIFA for every answer
- F – Formula: write the equation as it appears on the sheet.
- I – Insert: put in the numbers (convert to standard units first).
- F – Fix: rearrange to make the unknown the subject.
- A – Answer: calculate and always give the unit.
Questions
Q1 (F) A smart meter measures energy in kilowatt-hours. Explain what 1 kilowatt-hour means. (2 marks)
Show answer
• It is the energy transferred (1)
• by an appliance with a power of 1 kW used for 1 hour (1)
(1 kWh = 3.6 × 106 J)
Q2 (F) A 3.0 kW kettle is used for 6 minutes (0.1 hours). Calculate the energy transferred in kWh.
Show solution
F: E = P t
I: E = 3.0 × 0.1
F: E is already the subject
A: 0.30 kWh
Q3 (F) Electricity costs 25p per kWh. Calculate the cost of boiling the kettle in Q2.
Show solution
Cost = energy × price per kWh
I: 0.30 × 25p
A: 7.5p
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Q4 (F) On Monday the meter reads 12 345.6 kWh. On Tuesday at the same time it reads 12 357.4 kWh. Calculate the energy used and the cost at 25p per kWh.
Show solution
Energy used: 12 357.4 − 12 345.6 = 11.8 kWh
Cost: 11.8 × 25p = 295p = £2.95
Q5 (F/H) The in-home display shows 2.3 kW being used. The mains p.d. is 230 V. Calculate the current.
Show solution
Convert first: 2.3 kW = 2300 W
F: P = V I
I: 2300 = 230 × I
F: I = 2300 ÷ 230
A: 10 A
Q6 (F/H) A TV left on standby uses 0.50 W all year (8760 hours). Calculate the yearly cost at 25p per kWh.
Show solution
Convert first: 0.50 W = 0.00050 kW
F: E = P t
I: E = 0.00050 × 8760
A: E = 4.38 kWh
Cost: 4.38 × 25p = 109.5p ≈ £1.10
Q7 (F/H) A 9.5 kW electric shower is used for 8 minutes. Calculate the energy transferred in kWh and the cost at 25p per kWh.
Show solution
Convert first: 8 minutes = 8 ÷ 60 = 0.1333 h
F: E = P t
I: E = 9.5 × 0.1333
A: E = 1.27 kWh (3 s.f.)
Cost: 1.267 × 25p = 31.7p ≈ 32p
Q8 (F/H) Convert the energy used by the shower in Q7 (1.27 kWh) into joules. Give your answer in standard form.
Show solution
Use: 1 kWh = 3.6 × 106 J
I: 1.267 × 3.6 × 106
A: 4.6 × 106 J (2 s.f.)
Check: 9500 W × 480 s = 4 560 000 J
Q9 (H) A bill has a standing charge of 50p per day plus 25p for each kWh used. In 30 days the home uses 300 kWh. Calculate the total bill.
Show solution
Energy cost: 300 × 25p = 7500p = £75.00
Standing charge: 30 × 50p = 1500p = £15.00
Total: £75.00 + £15.00 = £90.00
Q10 (H) Explain how a smart meter can help a family reduce their energy use, and why this is good for the environment. (4 marks)
Show answer
Marking points (any four):
• The display shows the power being used right now and the cost, so the family can see which appliances use the most energy (1)
• They can switch off appliances, avoid standby or use high-power appliances (like the shower or tumble dryer) for less time (1)
• Less energy used means lower bills (1)
• Less electricity needs to be generated, so fewer fossil fuels are burned (1)
• So less carbon dioxide is released, reducing global warming (1)
⚠️ Where students lose marks
- Using watts instead of kilowatts when calculating energy in kWh.
- Using minutes instead of hours for kWh – 8 minutes is 8 ÷ 60 hours, not 0.8 hours.
- Forgetting the standing charge, which is paid every day whatever energy is used.
- Mixing up pence and pounds in the final answer.
More devices: all 40 everyday devices · Energy · Electricity
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