Electrons emerge from an electron accelerator as a beam having a circular cross-section of diameter 3 mm. The beam current is 6 μA and electrons are travelling so fast that their speed can be taken as $\mathrm{c} = 3 \mathrm{x} {10}^8$ m/sec with an insignificant error. Electron density in the beam is :

• A

  $2.82 \mathrm{x} {10}^{11} {\mathrm{m}}^{-3}$

• B

  $1.77 \mathrm{x} {10}^{10} {\mathrm{m}}^{-3}$

• C

  $1.54 \mathrm{x} {10}^9 {\mathrm{m}}^{-3}$

• D

  $1.28 \mathrm{x} {10}^9 {\mathrm{m}}^{-3}$