For precision work a laboratory requires a standard resistor whose value should not vary by more than ±0.05 % over the temperature range 20 °C to 50 °C.
The following data are available at 20 °C:
• Resistance of a constantan wire sample = 10.000 Ω, temperature coefficient of resistivity = 0.000 1 °C⁻¹.
• Resistance of a nichrome wire sample = 10.000 Ω, temperature coefficient of resistivity = 0.000 4 °C⁻¹.
(i) For each material, calculate the maximum percentage change in resistance expected when the temperature rises from 20 °C to 50 °C.
(ii) On the basis of your calculations, decide which material is more suitable for the required standard resistor and justify your choice.
(iii) State one practical reason (other than temperature sensitivity) that might nevertheless favour the other material in certain applications.