The Physics Question Bank

Course: Combined Science + Separate Physics  |  Tier: Foundation + Higher  |  Equation sheet: given in the exam

The equation

power = potential difference × current    P = V I

Quantity	Symbol	Unit
power	P	watts
potential difference	V	volts (V)
current	I	amperes (A)

Rearranged: I = P ÷ V  |  V = P ÷ I  |  UK mains = 230 V

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.

Foundation: aim for Q1–8.   Higher: aim for Q4–10. Most questions need rearranging.

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Questions

Q1 (F) A car headlamp runs on 12 V with a current of 2 A. Calculate its power.

Show solution

F: P = V I
I: P = 12 × 2
F: P is already the subject
A: 24 W

Q2 (F) A 2300 W kettle runs on the 230 V mains. Calculate the current.

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F: P = V I
I: 2300 = 230 × I
F: I = 2300 ÷ 230
A: 10 A

Q3 (F) A 60 W lamp draws a current of 0.5 A. Calculate the p.d. across it.

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F: P = V I
I: 60 = V × 0.5
F: V = 60 ÷ 0.5
A: 120 V

Q4 (F) A 1.15 kW toaster runs on the 230 V mains. Calculate the current.

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Convert first: 1.15 kW = 1150 W
F: P = V I
I: 1150 = 230 × I
F: I = 1150 ÷ 230
A: 5 A

Q5 (F) A 2.5 W USB fan runs on 5 V. Calculate the current in mA.

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F: P = V I
I: 2.5 = 5 × I
F: I = 2.5 ÷ 5 = 0.5 A
A: 500 mA

Q6 (F/H) A 1.8 kW hairdryer runs on 230 V. Fuses come in 3 A, 5 A and 13 A. Which fuse should it have?

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Convert first: 1.8 kW = 1800 W
F: P = V I
I: 1800 = 230 × I
F: I = 1800 ÷ 230 = 7.8 A
A: choose the next fuse above the normal current: 13 A

Q7 (F/H) A 7.2 kW home electric-car charger runs on 240 V. Calculate the current.

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Convert first: 7.2 kW = 7200 W
F: P = V I
I: 7200 = 240 × I
F: I = 7200 ÷ 240
A: 30 A

Q8 (F/H) A National Grid cable transmits 2.0 × 10⁸ W at 4.0 × 10⁵ V. Calculate the current.

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F: P = V I
I: 2.0 × 10⁸ = 4.0 × 10⁵ × I
F: I = 2.0 × 10⁸ ÷ 4.0 × 10⁵
A: 5.0 × 10² A

Q9 (H) A 230 V heater has a resistance of 23 Ω. Calculate its power.

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Step 1 – current
F: V = I R
I: 230 = I × 23
F: I = 230 ÷ 23 = 10 A
Step 2 – power
F: P = V I
I: P = 230 × 10
A: 2300 W

Q10 (H) A laptop charger supplies 65 W at 19.5 V. Calculate the current, to 2 significant figures.

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F: P = V I
I: 65 = 19.5 × I
F: I = 65 ÷ 19.5
A: 3.33… = 3.3 A (2 s.f.)