The magnetic field at the centre of a current carrying circular loop of radius $R$ is $16 \mu \mathrm{~T}$. The magnetic field at a distance $x=\sqrt{3} R$ on its axis from the centre is \_\_\_\_ $\mu \mathrm{T}$.

JEE Main · 2026 · 28 Jan 2026 · Shift 1 · Magnetic Effects of Current

The magnetic field at the centre of a current carrying circular loop of radius

R

16 μ T

. The magnetic field at a distance

x = 3 R

on its axis from the centre is ____

μ T

(A) $22$
(B)4
(C)2✓ Correct
(D)8

Answer: (C)

Solution

Magnetic field at the centre:

B_{0} = \frac{μ _{0} I}{2 R} = 16 μ T

Magnetic field on axis at distance

x

B = \frac{μ _{0} I R ^{2}}{2 ( x ^{2} + R ^{2} ) ^{3/2}}

For

x = 3 R

B = \frac{μ _{0} I R ^{2}}{2 ( 3 R ^{2} + R ^{2} ) ^{3/2}} = \frac{μ _{0} I R ^{2}}{2 ( 4 R ^{2} ) ^{3/2}} = \frac{μ _{0} I R ^{2}}{2 \times 8 R ^{3}} = \frac{μ _{0} I}{16 R}

Since

\frac{μ _{0} I}{2 R} = 16 μ T

, we have

B = \frac{16}{8} = 2 μ T

JEE Main · 2026 · 28 Jan 2026 · Shift 1 · Single correct option

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