Define strain energy and derive the equa-
tion for the same.

Explanation

When a wire is put under a tensile stress, work
is done against the inter atomic forces, This
work is stored in the form of "Eladtic potential
energy."
Experession to elastic potential energy : To
stretch a wire, force is applied As a result it
elongates. So the force applied is useful to
do some work This work is stored in it as
potential energy. When the deforming force
is removed, this energy is liberated as heat
The energy developed in a body (string)
when it is strained is called strain energy.
Let a force F be applied on awire fixed
at the upper end. Let extension be dl.
`therefore"Work done"=dW=Fdl`
Total work done in stretcing from
`0"to l"W=int_(0)^(l)dw=int_(0)^(l)fdl`
`thereforeWint_(0)^(l)(Yal^(2))/(L)=(1)/(2)(Yal)/(L).l`
`[becauseF=(Yal)/(L)]`
`W=(1)/(2)xx("stretching force"xx"elongation")/(AxxL)`
`therefore`Work done per unit volume
`=(1)/(2)xx"stress"xx"strain"`