Nichrome has a much higher resistivity than copper, yet nichrome — not copper — is used as the heating element in electric toasters. Justify this choice by comparing the relevant properties of the two materials.
Generated by claude-sonnet-4-6 · 2026-06-26 01:10 · grounding rag
Model Answer
Nichrome is preferred over copper as a heating element due to the following reasons:
- High resistivity: Nichrome has resistivity $100 \times 10^{-6}$ Ω m, far greater than copper's $1.62 \times 10^{-8}$ Ω m. Higher resistivity means more heat is generated (by Joule's heating, $H = I^2Rt$) for the same current.
- Does not oxidise at high temperatures: Alloys like nichrome do not burn or oxidise readily at high temperatures, making them suitable for repeated heating.
- Copper's low resistivity makes it an excellent conductor but a poor heat generator, so it is used for transmission lines, not heating devices.
Source: Chapter 11, Section 11.5 (Table 11.2) and Section 11.7.1
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Explanation
Examiners expect two clear points: (i) high resistivity → more heat generated, with values from Table 11.2 as evidence, and (ii) alloys don't oxidise at high temperatures. Mentioning Joule's heating formula adds precision. Avoid writing lengthy paragraphs — crisp, labelled points score better in 3-mark answers.