Magnetic Effects & Magnetism

JEE Main level, single correct, medium

99 of 276

Question 99 of 276

A long straight wire of radius ' aa ' caries a steady current i\mathrm{i}. The current is uniformly distributed across its cross section. The ratio of the magnetic field at a2\frac{a}{2} and 2a2 a is

Show answer and solution

Answer: (C) 11

B2πa2=μ0iπa2(πa24)\mathrm{B} 2 \pi \frac{\mathrm{a}}{2}=\mu_0 \frac{\mathrm{i}}{\pi \mathrm{a}^2}\left(\frac{\pi \mathrm{a}^2}{4}\right)
B1=μ0i4πa…\mathrm{B}_1=\frac{\mu_0 \mathrm{i}}{4 \pi \mathrm{a}} \quad \ldots (i)
B22π(2a)=μ0i\mathrm{B}_2 2 \pi(2 \mathrm{a})=\mu_0 \mathrm{i}
B2=μ0i4πa…(ii)\mathrm{B}_2=\frac{\mu_0 \mathrm{i}}{4 \pi \mathrm{a}} \quad \dots (ii)
B1 B2=1\frac{\mathrm{B}_1}{\mathrm{~B}_2}=1

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.

More Physics practice

JEE Main Physics practice question on Magnetic Effects & Magnetism (Magnetic Field), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.