CBSE Class 12 Physics 2014 Outside Delhi Set 1 Paper

Question : 14 of 30

Marks: +1, -0

Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area

1.0 \times 10^{-7} \mathrm{m}^2

carrying a current of

1.5 \mathrm{A}

. Assume the density of conduction electrons to be

9 \times 10^{28}

\mathrm{m}^{-3}

Solution:

v_d = \frac{I}{n A q} \; \text{, where} \;

I is the current

n

is charge density

q

is the charge of electron and

A

is the cross sectional area

\; v_d = \; \frac{1.5}{9 \times 10^{28} \times 1.0 \times 10^{-7} \times 1.6 \times 10^{-19}}

\; v_d = 10.4 \times 10^{-4} \mathrm{m} / \mathrm{sec}

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