Current Electricity

JEE Main level, single correct, medium

34 of 380

Question 34 of 380

Drift speed of electrons, when 1.5A1.5A current flows in a copper wire of cross section 5mm25{mm}^{2} is vd.{v}_{d}. If the electron density in copper is 9×1028m−39\times {10}^{28}{m}^{-3} the value of vd{v}_{d} in mms−1mm{s}^{-1} is close to (Take charge of an electron to be =1.6×10−19C=1.6\times {10}^{-19}C)

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Answer: (D) 0.020.02

Given,
Current, i=1.5Ai=1.5A,
Cross-section of the wire, A=5×10−6m2A=5\times {10}^{-6}{m}^{2} and
Electron density, n=9×1028m−3n=9\times {10}^{28}{m}^{-3}.
As current, i=neAvdi=neA{v}_{d}

⇒1.5=9×1028×1.6×10−19×5×10−6×vd\Rightarrow 1.5=9\times {10}^{28}\times 1.6\times {10}^{-19}\times 5\times {10}^{-6}\times {v}_{d}

⇒vd=0.02mms−1\Rightarrow {v}_{d}=0.02 mm{s}^{-1}.

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