Q. From Ampere's circuital law for a long straight wire of circular cross section carrying a steady current, the variation of magnetic field in the inside and outside region of the wire is :
A) a linearly decreasing function of distance upto the boundary of the wire and then a linearly increasing one for the outside region.
B) uniform and remains constant for both the regions.
C) a linearly increasing function of distance upto the boundary of the wire and then decreasing outside region.
D) a linearly increasing function of distance r upto the boundary of the wire 1/r dependence for the outside region.
Explanation
[Solution] Inside: $B = \frac{\mu_0 I r}{2\pi R^2} \propto r$; outside: $B = \frac{\mu_0 I}{2\pi r} \propto 1/r$. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.