Define electrical resistivity of a material. A copper wire and a nichrome wire have exactly the same dimensions. Can you use the resistance of these wires alone (without knowing the material) to compare the materials? Explain why resistivity is a more suitable property for this comparison.
Generated by claude-sonnet-4-6 · 2026-06-26 01:10 · grounding rag
Model Answer
Electrical resistivity is the resistance offered by a material of unit length and unit cross-sectional area. It is given by $\rho = \frac{RA}{l}$, with SI unit ohm-metre (Ω m).
Yes, since both wires have identical dimensions (same $l$ and $A$), the wire with higher resistance is the poorer conductor. However, resistance depends on dimensions too. Resistivity is an intrinsic property of the material, independent of shape or size — making it more suitable for comparing materials directly.
Source: Chapter 11, Section 11.5 – Factors on which the resistance of a conductor depends
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Explanation
- Define resistivity using the formula $\rho = RA/l$ and state its unit (Ω m) — this alone is worth 1 mark.
- For the second part, acknowledge that yes, since dimensions are identical, resistance comparison works here, but then explain why resistivity is better: it is a material property independent of dimensions. This distinction is what examiners look for in the second mark.
- Don't write lengthy explanations — two focused points are enough for 2 marks.