Current Electricity

JEE Main level, single correct, medium

26 of 380

Question 26 of 380

A current of 10A10A exists in a wire of cross-sectional area of 5mm25{mm}^{2} with a drift velocity of 2×10−3ms−1.2\times {10}^{-3}{ms}^{-1}. The number of free electrons in each cubic meter of the wire is

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Answer: (B) 625×1025625\times {10}^{25}

i=10A,A=5mm2=5×10−6m2i=10A,A=5{mm}^{2}=5\times {10}^{-6}{m}^{2} and vd=2×10−3ms−1{v}_{d}=2\times {10}^{-3}m{s}^{-1}
We know, i=neAvdi=neA{v}_{d}
∴10=n×1.6×10−19×5×10−6×2×10−3∴10=n\times 1.6\times {10}^{-19}\times 5\times {10}^{-6}\times 2\times {10}^{-3}
⇒n=0.625×1028=625×1025\Rightarrow n=0.625\times {10}^{28}=625\times {10}^{25}

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