A round uniformly tapered bar of length L and Young’s modulus E has diameter of ‘a’ at one end and ‘2d’ at the other end. If the bar is pulled by an axial force F, the extension produced will be

A

$$\frac{2FL}{(\pi E d^2)}$$

B

$$\frac{4FL}{(\pi E d^2)}$$

C

$$\frac{8FL}{(\pi E d^2)}$$

D

$$\frac{16FL}{(\pi E d^2)}$$