Q. At room temperature, copper has free electron density of $8.4 \times 10^{28}$ per $m^{3}.$ The copper conductor has a cross-section of $10^{- 6}m^{2}$ and carries a current of $5.4\ A.$ The electron drift velocity in copper is
A) $400\ m/s$
B) $0.4\ m/s$
C) $0.4\ mm/s$
D) $72\ m/s$
Explanation
(c) $V_{d} = \frac{i}{nAe} = \frac{5.4}{8.4 \times 10^{28} \times 10^{- 6} \times 1.6 \times 10^{- 19}}$
$= 0.4 \times 10^{- 3}\ m/sec = 0.4\ mm/sec$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.