Q. A potential difference of $V$ is applied at the ends of a copper wire of length $l$ and diameter $d$. On doubling only $d$, the drift velocity,
A) Becomes two times
B) Becomes half
C) Does not change
D) Becomes one-fourth
Explanation
(c) $v_{d} = \frac{I}{nAl} = \frac{1}{nAe} \times \frac{V}{R}$
$= \frac{1}{nAe} \times \frac{V}{(\rho l/A)} = \frac{V}{ne\rho l}$
As $v_{d}$ is independent of area of cross-section hence drift velocity will not change, when diameter is doubled
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.