Question 1Warm-upFoundation
A current of 2 A flows through a 6 Ω resistor. Calculate the potential difference across it.
V = I × R.
Worked solution
- V
Answer: V
GCSE & IGCSE physics practice
Ohm's law questions and answers
Potential difference = current × resistance: , with in volts, in amps and in ohms (Ω). For an ohmic conductor at constant temperature the resistance stays the same, so current is proportional to potential difference. A filament lamp's resistance rises as it heats up.
8 questions · Foundation tier · Every answer is checked as you type it, with a full worked solution. Updated .
Where ohm's law comes up
| GCSE (AQA) | Physics and Combined Science, Foundation and Higher. Recall V = IR (on AQA's list of equations to learn). Investigating I–V characteristics and resistance are required practicals. |
|---|---|
| Cambridge IGCSE (0625) | Core: recall and use R = V ÷ I, and describe an experiment to find resistance. Supplement: I–V graphs for a resistor, filament lamp and diode. |
The method
- V = I × R. Rearranged: I = V ÷ R and R = V ÷ I.
- mA ÷ 1000 = A; kΩ × 1000 = Ω.
- For a lamp, work out R at each reading: it isn't constant.
Ohm's law questions
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Warm-up
Question 2Warm-upFoundation
The potential difference across a component is 12 V and the current is 3 A. Calculate its resistance.
R = V ÷ I.
Worked solution
- Ω
Answer: Ω
Exam-style
Question 3Exam-styleFoundation
A 46 Ω heater is connected to 230 V. Calculate the current.
I = V ÷ R.
Worked solution
- A
Answer: A
Question 4Exam-styleFoundation
A current of 20 mA flows through a 150 Ω resistor. Calculate the potential difference.
20 mA = 0.02 A.
Worked solution
- V
Answer: V
Question 5Exam-styleFoundation
A 4.5 kΩ resistor is connected to 9 V. Calculate the current in amps.
4.5 kΩ = 4500 Ω.
Worked solution
- A
Answer: A (2 mA)
Question 6Exam-styleFoundation
A resistor has 3 V across it and 0.25 A through it. Calculate its resistance.
R = V ÷ I.
Worked solution
- Ω
Answer: Ω
Challenge
Question 7ChallengeFoundation
A filament lamp has 0.4 A at 2 V and 0.75 A at 6 V. Calculate its resistance at 6 V.
Use the readings at 6 V.
Worked solution
- At 2 V: Ω
- At 6 V: Ω
Answer: Ω (it was Ω at 2 V: resistance rises as the filament heats up)
Question 8ChallengeFoundation
A 15 Ω resistor has 0.4 A through it. The current is doubled. What is the new potential difference across the resistor?
The resistance stays the same, so V doubles too.
Worked solution
- At first: V
- New current A: V
Answer: V
Common mistakes
- Using milliamps as amps.
- Rearranging the wrong way (R = I ÷ V).
- Assuming a filament lamp has one fixed resistance.
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Sources
The questions are our own. The “where it comes up” notes are from each board's published specification, checked on 27 October 2026:
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