Q. A wire of diameter $0.02\ metre$ contains $10^{28}$ free electrons per cubic metre. For an electrical current of $100\ A,$ the drift velocity of the free electrons in the wire is nearly
A) $1 \times 10^{- 19}m/s$
B) $5 \times 10^{- 10}m/s$
C) $2 \times 10^{- 4}m/s$
D) $8 \times 10^{3}m/s$
Explanation
(c) By using $v_{d} = \frac{i}{neA} = \frac{100}{10^{28} \times 1.6 \times 10^{- 19} \times \frac{\pi}{4} \times (0.02)^{2}}$
$= 2 \times 10^{- 4}\ m/sec$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.