The amount of workdone in increasing the length of a wire through 1cm will be
YA2L
YL2A
YL22A
zero
W=12×stress×strain×volume
=12×(Y×strain)×strain×volume=12×Y×(strain)2×volume
=12Y(ℓ/L)2AL
=12(YA/L)ℓ2=12(YA/L)(1)2=YA2L