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Question: Answered & Verified by Expert
At room temperature, copper has free electron density of $8.4 \times 10^{28} \mathrm{~m}^{-3}$. The electron drift velocity in a copper conductor of cross-sectional area of $10^{-6} \mathrm{~m}^2$ and carrying a current of 5.4 A , will be
PhysicsCurrent ElectricityJIPMERJIPMER 2010
Options:
  • A $4 \mathrm{~ms}^{-1}$
  • B $0.4 \mathrm{~ms}^{-1}$
  • C $4 \mathrm{~cm} \mathrm{~s}^{-1}$
  • D $0.4 \mathrm{~mm} \mathrm{~s}^{-1}$
Solution:
1047 Upvotes Verified Answer
The correct answer is: $0.4 \mathrm{~mm} \mathrm{~s}^{-1}$
Drift velocity in a copper conductor
$\begin{aligned}
v_d=\frac{i}{n e A} & =\frac{5.4}{8.4 \times 10^{28} \times 1.6 \times 10^{-19} \times 10^{-6}} \\
& =0.4 \times 10^{-3} \mathrm{~ms}^{-1} \\
& =0.4 \mathrm{mms}^{-1}
\end{aligned}$

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