Fig. shows a wire of length l and of slightly non-uniform cross-section. Its radius at one end is R₁ and at  the other, it is R₂
The wire is stretched by forces F and F applied along the length in opposite directions and normal to the ends. Y being the Young's rpodulus, extension caused in the wire is nearly:

. 

• A

  $\frac{\mathrm{Fl}}{{\mathrm{\pi YR}}_1{\mathrm{R}}_2}$

• B

  $\frac{\mathrm{FlY}}{{\mathrm{R}}_1{\mathrm{R}}_2}$

• C

  $\frac{\mathrm{FlY}}{{\mathrm{\pi R}}_1^2{\mathrm{R}}_2^2}$

• D

  $\frac{\mathrm{FY}}{{\mathrm{l\pi R}}_1{\mathrm{R}}_2}$