A thin metal wire of length l increases in length by 0.1 on heating it from temperature θ1 to θ2. If a plate of same material is heated from θ1 to θ2 , which has dimensions 2l×3l then percentage increase in its area is:
ΔL=0.1
ΔL=L×ΔT
0.1=L×(θ2−θ1)
L×0.1θ2−θ1
For plate 2L×3l
ΔL=2L×ΔT
ΔL=2×L0.1(θ2−θ1)×(θ2−θ1)
=0.2L
Δw=0.3L
Δ/AA=ΔLL+Δww=0.2L2L+0.3L3L
=0.1+0.1=0.2