A s both steel rod and metal scale expands at 25°C, we use True value of length of rod at 25°C = Scale reading ×(1+α(θ′−θ)) where, α = coefficient of linear expansion of scale (=20×10−6/∘C) θ′= temperature at which observation is taken (=25∘Cr) and θ = temperature at which metre scalc reads correctly (= 0°C) Substituting values in Eq. (i), we get Length of rod at 25°C =1×[1+20×10−6(25−0)] =1+5×10−4=1.0005m Now, if l2= length of steel rod at 25∘C and l1= length of steel rod at 0∘C, then we have l2=l1(1+α∆θ) Substituting values, we have
