H1 Physics 8867 · Nov 2023PhysicsPaper 2Widespread errors
Paper 2 Q1 — p.d., e.m.f. and the thermistor divider
D.C. circuits — definitions per unit charge; thermistor in a potential divider
What the examiners said
“Weaker responses did not refer to a unit charge… incorrect ideas about potential difference flowing through a component… Some candidates incorrectly referred to a force being applied to a unit charge… A common error was to use the resistance of the thermistor in the numerator of the resistance ratio… many did not develop their answer further.”
Item 1 — defining potential difference
Which statement best defines the potential difference across a component?
Examiner report: “Weaker responses did not refer to a unit charge; some described p.d. flowing through a component.”
Item 2 — the divider calculation
A battery of e.m.f. 6.0 V (negligible internal resistance) is connected across a thermistor (resistance 1840 Ω at room temperature) in series with a 560 Ω fixed resistor. What is the p.d. across the fixed resistor?
Examiner report: “A common error was to use the resistance of the thermistor in the numerator of the resistance ratio.”
Item 3 — developing the explanation fully
The temperature of the thermistor now rises. Which is the complete chain of reasoning for what happens to the p.d. across the fixed resistor?
Examiner report: “Many demonstrated good understanding but did not develop their answer further.”
Explore — heat the thermistor
Slide the temperature. Watch the thermistor’s resistance fall, the current rise, and the 6.0 V redistribute between the two components.
At 20 °C this reproduces the exam values: 1840 Ω and 1.4 V across the fixed resistor. Heat it and the fixed resistor’s share climbs — the full four-link explanation in Item 3.
Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Physics 8867 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.
Made by lookang, using Claude Fable 5. More resources: iwant2study.org