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A metallic wire has a cross-sectional area of $1\,\text{cm}^2$ and contains $3\times 10^{28}$ charge carriers per cubic metre. If a current of $24\,\text{mA}$ flows through it, what is the drift speed of the carriers?
- $5\times 10^{-2}\,\text{m/s}$
- $0.5\,\text{m/s}$
- $5\times 10^{-3}\,\text{m/s}$
- $5\times 10^{-6}\,\text{m/s}$
Correct answer: $5\times 10^{-6}\,\text{m/s}$
Solution
The drift speed is found from $I=nAev_d$. Substituting the given values in SI units gives a very small speed, of order $10^{-6}\,\text{m/s}$.
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