Q1. [3] deep initial-understanding
A student needs a wire with very high resistance for use in an electric heating device. She has two wires of identical dimensions — one made of copper and one made of nichrome. (a) Which wire should she choose, and why? (b) State one property of nichrome, other than high resistivity, that makes it suitable for use in heating devices.
Generated by claude-sonnet-4-6 · 2026-06-26 01:07 · grounding rag
Model Answer
(a) She should choose the nichrome wire. Nichrome has a very high resistivity ($100 \times 10^{-6}$ Ω m), much greater than copper ($1.62 \times 10^{-8}$ Ω m). Since resistance $R = \rho\, l/A$ and both wires have identical dimensions, the nichrome wire will have far greater resistance, producing more heat.
(b) Nichrome (an alloy) does not oxidise (burn) readily at high temperatures, which makes it durable and long-lasting in heating devices.
Source: Chapter 11, Section 11.5 – Factors on which resistance depends
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Explanation
- Part (a) is worth 2 marks: name the correct wire and justify using resistivity values/formula. Examiners expect both.
- Part (b) is worth 1 mark: the key phrase from the textbook is "alloys do not oxidise readily at high temperatures." Write it clearly. Do not repeat resistivity (the question says "other than high resistivity").
- Quoting the actual resistivity values (or at least saying nichrome's is much higher) strengthens part (a).