The conduction-electron number density in copper is $8.0 \times 10^{28}\,\text{m}^{-3}$. For a copper wire with diameter $0.42\,\text{mm}$ carrying a current of $0.57\,\text{A}$, what is the mean drift speed of the electrons?
- A$8.0 \times 10^{-11}\,\text{m s}^{-1}$
- B$3.2 \times 10^{-10}\,\text{m s}^{-1}$
- C$8.0 \times 10^{-5}\,\text{m s}^{-1}$
- D$3.2 \times 10^{-4}\,\text{m s}^{-1}$