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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumApplication

JEE Main 17 March 2021, Shift 2, Physics Q12

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

A hairpin like shape as shown in figure is made by bending a long current carrying wire. What is the magnitude of a magnetic field at point P which lies on the centre of the semicircle ?

The figure, in words

Two long parallel straight wires, upper one with an arrow pointing right (labelled I) and lower one with an arrow pointing left (labelled I), joined at their right ends by a semicircle drawn as a dotted arc; a radius labelled r is drawn from the centre (dot) to the arc, with a current arrow marked I at the right of the semicircle. Point P is labelled at the left of the centre, inside the semicircle.
  1. (1)μ0I2πr(2−π)\frac{\mu_0 \mathrm{I}}{2\pi \mathrm{r}}(2-\pi)
  2. (2)μ0I2πr(2+π)\frac{\mu_0 \mathrm{I}}{2\pi \mathrm{r}}(2+\pi)
  3. (3)μ0I4πr(2+π)\frac{\mu_0 \mathrm{I}}{4\pi \mathrm{r}}(2+\pi)Official answer
  4. (4)μ0I4πr(2−π)\frac{\mu_0 \mathrm{I}}{4\pi \mathrm{r}}(2-\pi)

Official answer

Option 3

NTA final key.

Chapter
Moving Charges and Magnetism
Topic
Biot-Savart Law
Idea tested
Field of a Hairpin Loop

Same topic in other shifts

All Biot-Savart Law questions
  1. 2 Apr 2026, Shift 1 · Q39Two identical long current carrying wires are bent into the shapes shown in the following figures. If the magnitude of magnetic fields at…MediumSingle correctHas a figure
  2. 6 Apr 2026, Shift 1 · Q42A small cube of side 1 mm is placed at the centre of a circular loop of radius 10 cm carrying a current of 2 A. The magnetic energy stored…MediumSingle correct
  3. 6 Apr 2026, Shift 2 · Q38A current of 30 A each flows in opposite directions in two conducting wires, placed parallel to each other at a distance of 8 cm. The…EasySingle correct
  4. 2 Apr 2025, Shift 1 · Q38Let B1B_1 be the magnitude of magnetic field at center of a circular coil of radius R carrying current I. Let B2B_2 be the magnitude of…EasySingle correct
  5. 2 Apr 2025, Shift 2 · Q27Given a charge qq, current II and permeability of vacuum μ0\mu_0. Which of the following quantity has the dimension of momentum ?MediumSingle correct
  6. 3 Apr 2025, Shift 1 · Q48A loop ABCDA, carrying current I=12\mathrm{I} = 12 A, is placed in a plane, consists of two semi-circular segments of radius…MediumNumerical valueHas a figure

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. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.