Practise Current, resistance and potential difference. 20 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Required practical:Resistance (method, variables and exam tips)
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Write down the equation that links current (I), potential difference (V) and resistance (R).
V = I R
A current of 0.20 A flows through a component of resistance 25 Ω. Calculate the potential difference across the component. Use the equation: potential difference = current × resistance
5.0 V
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
A resistor is connected to a battery.
(a) What is the unit of resistance? Tick (✓) one box.[1]
ampere
ohm
volt
watt
(b) The current in the resistor is 0.50 A. The resistance of the resistor is 12 Ω. Calculate the potential difference across the resistor. Use the equation: potential difference = current × resistance[2]
(c) The resistor is replaced with a resistor that has a greater resistance. The potential difference across it stays the same. What happens to the current in the resistor? Tick (✓) one box.[1]
It decreases.
It increases.
It stays the same.
Show the answer and mark scheme
(a)Answer: ohm
(b)Answer: 6.0 V
V = 0.50 × 12
V = 6.0 (V)
(c)Answer: It decreases.
Question 2Medium7 marks
Electrical components have resistance.
(a) Write down the equation that links current (I), potential difference (V) and resistance (R).[1]
(b) The potential difference across the heating element of a kettle is 230 V. The current in the element is 4.6 A. Calculate the resistance of the heating element.[3]
(c) The current in a 150 Ω resistor is 20 mA. Calculate the potential difference across the resistor.[3]
Show the answer and mark scheme
(a)Answer: V = I R
V = I × R / potential difference = current × resistance
(b)Answer: 50 Ω
230 = 4.6 × R
R = 230 ÷ 4.6
R = 50 (Ω)
(c)Answer: 3.0 V
I = 0.020 A
V = 0.020 × 150
V = 3.0 (V)
Question 3Hard7 marks
A heating element is made from a wire that has a resistance of 0.80 Ω for each metre of its length. The element is connected to a 12 V power supply.
(a) The current in the element must be 1.5 A. Calculate the length of wire needed.[3]
(b) The wire is cut into two equal halves. One half is connected to the 12 V supply. Calculate the current in this half of the wire.[2]
(c) The current in the element decreases slightly in the first few seconds after it is switched on. Explain why.[2]
Show the answer and mark scheme
(a)Answer: 10 m
12 = 1.5 × R
R = 8.0 (Ω)
length = 8.0 ÷ 0.80 = 10 (m)
(b)Answer: 3.0 A
R = 4.0 (Ω)
I = 12 ÷ 4.0 = 3.0 (A)
(c)Answer: The wire gets hotter, so its resistance increases; with the same potential difference, the current decreases.
the wire gets hotter / temperature increases, so its resistance increases
(so) for the same potential difference the current is smaller