A copper wire has a square cross-section, $2.0\, mm$ on a side. It carries a current of $8\, A$ and the density of free electrons is $8 \times {10^{28}}\,{m^{ - 3}}$. The drift speed of electrons is equal to
  • A$0.156 × {10^{ - 3}}\,  m.s^{-1}$ 
  • B$0.156 × {10^{ - 2}} \, m.s^{-1}$ 
  • C$3.12 × {10^{ - 3}} \, m.s^{-1}$ 
  • D$3.12 × {10^{ - 2}} \, m.s^{-1}$ 
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