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Saturday, 31 October

JEE Main 2025 · PhysicsMultiple choiceDiagram basedHardMulti-step

JEE Main 8 April 2025, Shift 2, Physics Q39

Question 39 of 75 in this shift, Physics question 14 of 25, Section A.

Figure shows a current carrying square loop ABCD of edge length is 'a' lying in a plane. If the resistance of the ABC part is r and that of ADC part is 2r, then the magnitude of the resultant magnetic field at centre of the square loop is

The figure, in words

Square loop ABCD drawn as a diamond: current I enters at A (left) and leaves at C (right); upper path A-B-C carries current i1i_1, lower path A-D-C carries i2i_2; side length a marked on BC; centre of the square marked with a dot.
  1. (1)2μ0I3πa\frac{\sqrt{2}\mu_0 I}{3\pi a}Official answer
  2. (2)3πμ0I2a\frac{3\pi\mu_0 I}{\sqrt{2}a}
  3. (3)μ0I2πa\frac{\mu_0 I}{2\pi a}
  4. (4)2μ0I3πa\frac{2\mu_0 I}{3\pi a}

Official answer

Option 1

NTA final key.

Chapter
Moving Charges and Magnetism
Topic
Biot-Savart Law
Idea tested
Field at Center of Regular Polygon

Same idea in other shifts

Asked 5× in all
  1. 1 Feb 2024, Shift 1 · Q57A regular polygon of 6 sides is formed by bending a wire of length 4π4\pi meter. If an electric current of 4π34\pi\sqrt{3} A is flowing…MediumNumerical value
  2. 30 Jan 2024, Shift 2 · Q57The current of 5A flows in a square loop of sides 1 m1\ m is placed in air. The magnetic field at the centre of the loop is…EasyNumerical value
  3. 31 Aug 2021, Shift 2 · Q17A current of 1.5 A is flowing through a triangle, of side 9 cm each. The magnetic field at the centroid of the triangle is : (Assume that…MediumSingle correct
  4. 3 Sep 2020, Shift 1 · Q13Magnitude of magnetic field (in SI units) at the centre of a hexagonal shape coil of side 10 cm, 50 turns and carrying current I (Ampere)…MediumSingle 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. 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.