AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Exam Practice: Resistors and I–V characteristics
Resistors and I–V characteristics · Electricity · Lesson 3 of 10 · 21 marks · 22 minutes
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Instructions
• Answer all the questions.
• Write your answers in the spaces provided.
• The marks for each question are shown in brackets - use this as a guide to how much to write.
• The answers are on separate pages at the back. Attempt every question before you look at them.
• Answer all questions. Use the mark allocation as a guide to how much to write.
Question 1 COMPLETE (3 marks)
Name the component whose I–V characteristic shows current flowing in one direction only, and the component whose resistance decreases as the temperature increases. Then state what happens to the resistance of an LDR in bright light.
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(Total for Question 1 = 3 marks)
Question 2 USE THE GRAPH (4 marks)
The graph shows the I–V characteristic of a filament lamp. (a) Calculate the resistance of the lamp when the potential difference is 6.0 V. (b) The resistance at 2.0 V is 5.9 Ω. Explain why the resistance at 6.0 V is different.
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(Total for Question 2 = 4 marks)
Question 3 EXPLAIN (3 marks)
A thermistor is used in a circuit to control a heating system. Explain how the resistance of the thermistor changes as the room warms up.
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(Total for Question 3 = 3 marks)
Question 4 DESCRIBE (6 marks)
Describe how you would investigate the relationship between the current through a filament lamp and the potential difference across it. Include a circuit diagram description, the readings to take and how you would present and use the results.
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(Total for Question 4 = 6 marks)
Question 5 EXPLAIN (2 marks)
A student measures the resistance of a diode. Explain why the resistance is very high when the diode is connected the other way round.
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(Total for Question 5 = 2 marks)
Question 6 SUGGEST (3 marks)
An automatic outdoor light contains an LDR. Explain how the light switches on when it gets dark.
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(Total for Question 6 = 3 marks)
TOTAL FOR PAPER = 21 MARKS
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Answers and mark scheme
Check your answer only once you have written one.
Question 1 (3 marks)
A diode; a thermistor; the resistance of an LDR decreases in bright light.
• Diode 1 mark
• Thermistor 1 mark
• LDR resistance decreases 1 mark
Question 2 (4 marks)
(a) At 6.0 V the current is 0.62 A. R = 6.0 ÷ 0.62 = 9.7 Ω. (b) At 6.0 V the current is greater so the filament is hotter, and the resistance of the filament increases with temperature.
• Reads 0.62 A 1 mark
• 9.7 Ω 1 mark
• Higher current means higher temperature 1 mark
• Resistance increases with temperature 1 mark
Question 3 (3 marks)
As the temperature increases the resistance of the thermistor decreases, so the current through it increases and the potential difference across it changes; this is used to switch the heating off.
• Resistance decreases as temperature increases 1 mark
• Current or potential difference changes in the circuit 1 mark
• Used to switch the heating off 1 mark
Question 4 (6 marks)
See levels-of-response scheme.
• Level 3 (5 to 6 marks): a correct circuit (ammeter in series, voltmeter across the lamp, variable resistor or supply), a range of pd values and matching currents, a graph of I against V and a description of its shape or the changing gradient 5 to 6 marks
• Level 2 (3 to 4 marks): a method with the main apparatus and some readings; the graph is mentioned 3 to 4 marks
• Level 1 (1 to 2 marks): simple statements about measuring current and pd 1 to 2 marks
Question 5 (2 marks)
A diode has a very high resistance in the reverse direction, so almost no current flows.
• Very high resistance in reverse 1 mark
• Almost no current flows 1 mark
Question 6 (3 marks)
When it gets dark the resistance of the LDR increases. The pd across the LDR increases (or current decreases), which triggers the circuit that switches the light on.
• Resistance of LDR increases in the dark 1 mark
• Change in pd or current in the circuit 1 mark
• Circuit switches the light on 1 mark