JEE Main 2024 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 8 April 2024, Shift 2, Physics Q42

Question 42 of 90 in this shift, Physics question 12 of 30, Section A.

A long straight wire of radius a carries a steady current I. The current is uniformly distributed across its cross section. The ratio of the magnetic field at

\frac{a}{2}

and

2a

from axis of the wire is :

(1) $1:4$
(2) $3:4$
(3) $1:1$ Official answer
(4) $4:1$

Official answer

Option 3

NTA final key.

Chapter: Moving Charges and Magnetism
Topic: Ampere's Circuital Law
Idea tested: Field Inside Thick Wire

Same idea in other shifts

Asked 4× in all

25 Jun 2022, Shift 1 · Q40A long straight wire with a circular cross-section having radius R, is carrying a steady current I. The current I is uniformly distributed…EasySingle correct
27 Aug 2021, Shift 2 · Q11A coaxial cable consists of an inner wire of radius ‘a’ surrounded by an outer shell of inner and outer radii ‘b’ and ‘c’ respectively.…MediumSingle correct
9 Jan 2020, Shift 1 · Q12A long, straight wire of radius a carries a current distributed uniformly over its cross-section. The ratio of the magnetic fields due to…EasySingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.