Edexcel A-Level Physics Temperature and Resistance

Practise Edexcel A-Level Physics temperature effects on resistance using filament lamps, metal wires and negative-temperature-coefficient thermistors.

Exam points

explain filament-lamp or metal-wire resistance increases using lattice vibrations and collisions
predict thermistor current and voltmeter changes from temperature and conduction-electron changes
link resistor heating to increased resistance and lower power using P = V²/R or P = VI

[Maximum number: 3]

The circuit contains three identical resistors and switches X and Y. Each resistor is wire of diameter $0.181\,\mathrm{mm}$ and length $55.0\,\mathrm{cm}$ , with resistivity $1.10\times10^{-6}\,\Omega\,\mathrm{m}$ at room temperature.

Figure for Question 2.4.79 - Temperature effects on resistance question 1 — Edexcel A-Level Physics AS

Switch X was open and switch Y was closed.

After switch Y had been closed for a few minutes, the power dissipated by the resistor decreased.

Explain why.

The resistor temperature rises, so its resistance rises. Since $P=V^2/R$ for fixed supply voltage, the dissipated power decreases.

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2.4.79 - Temperature effects on resistance question 1