Q. Assume that each atom of copper contributes one free electron. What is the average drift velocity of conduction electrons in a copper wire of cross-sectional area $10^{- 7}\ m^{2}$, carrying a current of 1.5 A? (Given density of copper =$9 \times 10^{- 3}kgm^{- 3}$; atomic mass of copper =63.5; Avogadro’s number$= 6.023 \times 10^{23}$ per gram atom)
A) $1.1 \times 10^{- 2}ms^{- 1}$
B) $1.1 \times 10^{- 3}ms^{- 1}$
C) $2.2 \times 10^{- 2}ms^{- 1}$
D) $2.2 \times 10^{- 3}ms^{- 1}$
Explanation
(b) Number of free electrons per unit volume,
$n = \frac{N}{M}\rho = \frac{6.023 \times 10^{23}}{63.5 \times 10^{- 3}} \times 9 \times 10^{3}$
$\therefore\ v_{d} = \frac{i}{nAe}$
$= \frac{1.5 \times 63.5 \times 10^{- 3}}{6.023 \times 10^{23} \times 9 \times 10^{3} \times 10^{- 7} \times 1.6 \times 10^{- 19}}$
$= 1.1 \times 10^{- 3}ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.