The V – I graph for a conductor at temperature T1 and T2 are as shown in figure. Then (T2– T1) is equal to [α = temperature coefficient of resistivity]

According to Ohm’s Law, V = R.I. It means that ‘R’ is the slope of V – I graph.∴   R1=tanθ  and ∴   R2=R1  1+α T2−T1 ∴  cotθ  =  tanθ  1+α T2−T1 ⇒  α  T2−T1=cotθtanθ−1  ⇒  T2−T1=1α .  cos2θsin2θ = 1α  cos600sin2300=2α