# Drift speed of electrons, when 1.5 A of current flows in a copper wire of cross section 5 mm2, is v.

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Drift speed of electrons, when 1.5 A of current flows in a copper wire of cross section 5 mm2, is v. If the electron density in copper is 9 × 1028 /m3 the value of v in mm/s is close to (Take charge of electron to be = 1.6 × 10–19C)

(1) 0.2

(2) 3

(3) 2

(4) 0.02

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Ans: (4) 0.02

Sol: $I = neAv_d$

$\implies v_d={I\over neA}$

$={1.5\over9\times10^{28}\times1.6\times10^{-19}\times5\times10^{-6}}$

$=0.02\text{ m/s}$