Q119 / 160 · JIPMER 2013 · Physics

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

  • A
    $4 \mathrm{~ms}^{-1}$
  • B
    $0.4 \mathrm{~ms}^{-1}$
  • C
    $4 \mathrm{~cm} \mathrm{~s}^{-1}$
  • Correct answer
    D
    $0.4 \mathrm{~mm} \mathrm{~s}^{-1}$

Solution

Drift velocity in a copper conductor $\begin{aligned} v_d=\frac{i}{n e A} & =\frac{5.4}{8.4 \times 10^{28} \times 1.6 \times 10^{-19} \times 10^{-6}} \\ & =0.4 \times 10^{-3} \mathrm{~ms}^{-1} \\ & =0.4 \mathrm{mms}^{-1}\end{aligned}$

Hence, the correct answer is option: 'D'.

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