Question

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

Answer 1

Ans: (4) 0.02

Sol: $I = neAv_d$

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

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

$=0.02\text{ m/s}$