CBSE Class 12 Physics 2014 Outside Delhi Set 3 Paper

Question : 5

Total: 9

Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 2.5×10−7m2 carrying a current of 2.7A. Assume the density of conduction electrons to be 9×1028 m−3.

Solution:

We know that drift velocity, vd=‌

nAq

Where I is the current, n is charge density, q is charge of electron and A is cross-sectional area.

vd‌=‌

9×1028×2.5×10−7×1.6×10−19

vd‌=7.5×10−4m∕ s
or vd‌=0.75‌mm‌ s−1
This is the required average drift velocity.

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