Physics · Moving Charges and Magnetic Field

JEE Main 2026 — 24 January, Evening Shift — Question 32

Two identical circular loops P and Q each of radius r are lying in parallel planes such that they have common axis. The current through P and Q are I and 4I respectively in clockwise direction as seen from O . The net magnetic field at O is:

Option A:
$\frac{3 \mu_{\mathrm{o}} \mathrm{I}}{4 \sqrt{2 \mathrm{r}}}$ toward P
Option B:
$\frac{\mu_{\mathrm{o}} \mathrm{I}}{4 \sqrt{2} \mathrm{r}}$ toward P
Option C:
$\frac{\mu_{0} I}{4 \sqrt{2} r}$ towards $Q$
Option D:
$\frac{3 \mu_{0} I}{4 \sqrt{2} r}$ towards $Q$
Correct

Answer: D

Step-by-step solution

$B_{n e t}=B_{1}-B_{2}$ $=\frac{4 \mu_{0} i R^{2}}{2\left(R^{2}+R^{2}\right)^{3 / 2}}-\frac{\mu_{0} i R^{2}}{2\left(R^{2}+R^{2}\right)^{3 / 2}}$ $=\frac{3 \mu_{0} \mathrm{i}}{4 \sqrt{2} \mathrm{R}}$

Answer key and solution verified before publishing.

Practise Moving Charges and Magnetic Field

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Solve a similar one free

Exam: JEE Main 2026
Paper: 24 January, Evening Shift
Subject: Physics
Chapter: Moving Charges and Magnetic Field
Topic: Magnetic Field Due to Current-Carrying Wire - Biot-Savart Law