NEET 2026 — Physics solution

NEET2026Physics

The figure given below shows a long straight solid wire of circular cross-section of radius ‘a’ carrying steady current I. The current I is uniformly distributed across its cross-section. The plot which correctly represents the variation of magnetic field (B) with distance (r) from the axis of the conductor in the region is :

Solution

For a uniformly current-carrying solid wire:

Inside ( $r < a$ ): $B_{in} = \frac{μ _{0} I r}{2 π a ^{2}}$ , so $B \propto r$ (linear rise).

Outside ( $r > a$ ): $B_{o u t} = \frac{μ _{0} I}{2 π r}$ , so $B \propto 1/ r$ .

B grows linearly from 0 at the axis to a maximum at $r = a$ , then falls off as $1/ r$ outside — option (3).

← Back to full paper

Practice more Physics

Concept-wise practice with instant solutions on Fundamenthol.

Start practicing →