A wire of length L, area of cross section A is hanging from a fixed support. The length of the wire changes to ${\mathrm{L}}_1$ when mass M is suspended from its free end. The expression for Young's modulus is:

1. $\frac{\mathrm{Mg}({\mathrm{L}}_1-\mathrm{L})}{\mathrm{AL}}$

2. $\frac{\mathrm{MgL}}{{\mathrm{AL}}_1}$

3. $\frac{\mathrm{MgL}}{\mathrm{A}({\mathrm{L}}_1-\mathrm{L})}$

4. $\frac{{\mathrm{MgL}}_1}{\mathrm{AL}}$

When a block of mass M is suspended by a long wire of length L, the length of the wire becomes (L+l). The elastic potential energy stored in the extended wire is:

1. $\frac{1}{2}\mathrm{MgL}$

2. Mgl

3. MgL

4. $\frac{1}{2}\mathrm{Mgl}$