A nichrome wire is first tested at 20∘C and then at 120∘C. In each case a straight-line V-versus-I graph through the origin is obtained. The slope at 20∘C is found to be 3.5Ω while at 120∘C it rises to 5.0Ω.
(i) Calculate the percentage change in resistance of the wire between the two temperatures.
(ii) Using your result, determine the temperature coefficient of resistance α for nichrome in this temperature range.
(iii) Discuss briefly why the linearity of the V-versus-I graphs at both temperatures is important for the validity of your calculation in part (ii).