A current of 10 amperes is maintained in a conductor of cross-section of ${10}^{-4} {\mathrm{m}}^2$. If the electron density is $9 \mathrm{x} {10}^{28} {\mathrm{m}}^{-3}$, what is the drift velocity of free electrons ?

• A

  $6.9 \mathrm{x} {10}^{-6} {\mathrm{ms}}^{-1}$

• B

  $6.9 \mathrm{x} {10}^{-4} {\mathrm{ms}}^{-1}$

• C

  $6.9 \mathrm{x} {10}^5 {\mathrm{ms}}^{-1}$

• D

  None of these