Q72 / 90 · JEE Main 2021 (27 Jul Shift 2) · Physics

Figure $A$ and $B$ shown two long straight wires of circular cross-section ( $a$ and $b$ with $a < b$ ), carrying current $I$ which is uniformly distributed across the cross-section. The magnitude of magnetic field $B$ varies with radius $r$ and can be represented as:

Solution

Graph for wire of radius $R$ :

As $b > a$

$B_{a} > B_{b}$

$B_{a} = \frac{μ_{0} i}{2 π a}$

$B_{b} = \frac{μ_{0} i}{2 π b}$

Hence, the correct answer is option: 'C'.