A steel pipe is constructed of a material for which $$\mu_r = 200$$ and $$\sigma = 5 \times 10^6 mho/m$$. The outer and inner radii are 8 and 6 mm respectively and the length is 80 m. If the total current carried by the pipe is $$2 \cos10^4 \pi t A,$$ Then the skin depth will be

A

$$0.225 \times 10^{-3} m$$

B

$$0.300 \times 10^{-3} m$$

C

$$0.352 \times 10^{-3} m$$

D

$$0.125 \times 10^{-3} m$$