10 AQA GCSE Physics questions on current, resistance and potential difference (V = IR) that get harder as you go, from Foundation to Higher, each with a full worked solution.
Course: Combined Science + Separate Physics | Tier: Foundation + Higher | Equation sheet: given in the exam
📌 KEY DEFINITIONS – learn them word for word
Potential difference is the energy transferred per unit charge passing between two points. Unit: volt (V). 1 V = 1 joule per coulomb.
Resistance is the opposition to the flow of current in a component. Unit: ohm (Ω).
Ohmic conductor: the current is directly proportional to the potential difference at constant temperature, so its resistance stays the same.
The equation
potential difference = current × resistance V = I R
| Quantity | Symbol | Unit |
|---|---|---|
| potential difference | V | volts (V) |
| current | I | amperes (A) |
| resistance | R | ohms (Ω) |
Rearranged: I = V ÷ R | R = V ÷ I | 1 kΩ = 1000 Ω; 1 mA = 0.001 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.
Foundation: aim for Q1–8. Higher: aim for Q4–10. Most questions need rearranging.
Questions
Q1 (F) A current of 2 A flows through a 6 Ω resistor in a toy car. Calculate the potential difference across it.
Show solution
F: V = I R
I: V = 2 × 6
F: V is already the subject
A: 12 V
Q2 (F) A heater with a resistance of 46 Ω is connected to the 230 V mains. Calculate the current.
Show solution
F: V = I R
I: 230 = I × 46
F: I = 230 ÷ 46
A: 5 A
Q3 (F) A 9 V battery makes a current of 0.3 A flow through a lamp. Calculate the resistance of the lamp.
Show solution
F: V = I R
I: 9 = 0.3 × R
F: R = 9 ÷ 0.3
A: 30 Ω
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Q4 (F) An LED needs a p.d. of 3.0 V and a current of 20 mA. Calculate its resistance.
Show solution
Convert first: 20 mA = 0.020 A
F: V = I R
I: 3.0 = 0.020 × R
F: R = 3.0 ÷ 0.020
A: 150 Ω
Q5 (F) A 2.0 kΩ resistor in a phone circuit has 12 V across it. Calculate the current in mA.
Show solution
Convert first: 2.0 kΩ = 2000 Ω
F: V = I R
I: 12 = I × 2000
F: I = 12 ÷ 2000 = 0.006 A
A: 6 mA
Q6 (F/H) A 6 Ω and a 4 Ω resistor are connected in series to a 5 V battery. Calculate the current.
Show solution
Total resistance in series: 6 + 4 = 10 Ω
F: V = I R
I: 5 = I × 10
F: I = 5 ÷ 10
A: 0.5 A
Q7 (F/H) A thermistor in a fridge sensor has a resistance of 1.5 kΩ. A current of 4 mA flows through it. Calculate the p.d. across it.
Show solution
Convert first: 1.5 kΩ = 1500 Ω; 4 mA = 0.004 A
F: V = I R
I: V = 0.004 × 1500
F: V is already the subject
A: 6 V
Q8 (F/H) Dry human skin can have a resistance of 1.0 × 105 Ω. Calculate the current if someone touches a 230 V wire. Give your answer in standard form.
Show solution
F: V = I R
I: 230 = I × 1.0 × 105
F: I = 230 ÷ 1.0 × 105
A: 2.3 × 10−3 A
Q9 (H) 90 C of charge flows through a 20 Ω resistor in 30 s. Calculate the p.d. across the resistor.
Show solution
Step 1 – current
F: Q = I t
I: 90 = I × 30
F: I = 90 ÷ 30 = 3 A
Step 2 – p.d.
F: V = I R
I: V = 3 × 20
A: 60 V
Q10 (H) A 1.5 V AA cell makes a current of 0.28 A flow through a bulb. Calculate the bulb’s resistance, to 2 significant figures.
Show solution
F: V = I R
I: 1.5 = 0.28 × R
F: R = 1.5 ÷ 0.28
A: 5.357… = 5.4 Ω (2 s.f.)
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