CBSE Class 12 Physics 2014 Outside Delhi Set 3 Paper

Question : 5 of 9

Marks: +1, -0

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

2.5 \times 10^{-7} \text{ m}^2

carrying a current of

2.7 \text{ A}

. Assume the density of conduction electrons to be

9 \times 10^{28}

\text{m}^{-3}

Solution:

We know that drift velocity,

v_d=\frac{I}{n A q}

Where

I

is the current,

n

is charge density,

q

is charge of electron and A is cross-sectional area.

v_d=\frac{27}{9 \times 10^{28} \times 2.5 \times 10^{-7} \times 1.6 \times 10^{-19}}

v_d=7.5 \times 10^{-4} \text{ m/s}

v_d=0.75 \text{ mm s}^{-1}

This is the required average drift velocity.

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