The number density of free electrons in copper is $8.0 \times 10^{28}\,\text{m}^{-3}$. A copper wire has diameter $0.42\,\text{mm}$. Determine the average drift speed of the free electrons in the wire when the current in the wire is $0.57\,\text{A}$?
- 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$3.2 \times 10^{-4}\,\text{m s}^{-1}$