A wire of length L0 is supplied heat to raise its temperature by T. lf γ is the coefficient of volume expansion of the wire and Y is Young's modulus of the wire then the energy density stored in the wire is

Due to heating the length of the wire increases.∴Longitudinal strain is produced⇒ ΔLL=α×ΔTElastic potential energy per unit volume     E=12× Stress × Strain =12×Y×( Strain )2⇒E=12×Y×ΔLL2=12×Y×α2×ΔT2or E=12×Y×γ32×T2=118γ2YT2                                                [As γ=3α and ΔT=T (given) ]