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In the drift model of conduction, the average drift velocity v_d of electrons in a conductor of cross-section A carrying current I, where n is electron number density and e is electronic charge, is
Av_d = I · A / (n e)
Bv_d = n A / (I e)
Cv_d = I / (n e A)
Dv_d = n e A / I
Answer & Solution
Correct answer: C. v_d = I / (n e A)
I = n e A v_d ⇒ v_d = I / (n e A). Drift velocity for typical metals at ordinary currents is of the order of mm/s — surprisingly small.
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