Q. A copper wire of length 10 m and radius $(10^{-2}/\sqrt{\pi})$ m has electrical resistance of 10 Ω. The current density in the wire for an electric field strength of 10 V/m is :
A) $10^5\ A/m^2$
B) $10^4\ A/m^2$
C) $10^6\ A/m^2$
D) $10^{-5}\ A/m^2$
Explanation
[Solution] $A = \pi r^2 = 10^{-4}\ m^2$; $\rho = RA/l = 10 \times 10^{-4}/10 = 10^{-4}\ \Omega m$; $J = E/\rho = 10/10^{-4} = 10^5\ A/m^2$. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.