Physics · PYQ NEET UG 2022

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 linearly increasing function of distance r upto the boundary of the wire and then decreasing one with 1/r dependence for the outside region.
a linearly decreasing function of distance upto the boundary of the wire and then a linearly increasing one for the outside region.
uniform and remains constant for both the regions.
a linearly increasing function of distance upto the boundary of the wire and then linearly decreasing for the outside region.

Correct answer · Option 1

a linearly increasing function of distance r upto the boundary of the wire and then decreasing one with 1/r dependence for the outside region.

Inside a solid wire, \( B \propto r \) (increases linearly). Outside the wire, \( B \propto \frac{1}{r} \) (decreases with distance).