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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctHardMulti-step

JEE Main 5 September 2020, Shift 1, Physics Q15

Question 15 of 75 in this shift, Physics question 15 of 25.

A square loop of side 2a, and carrying current I, is kept in XZ plane with its centre at origin. A long wire carrying the same current I is placed parallel to the zz-axis and passing through the point (0, b, 0), (b > > a). The magnitude of the torque on the loop about zz-axis is given by :
  1. (1)2μoI2a2πb\frac{2\mu_o I^2 a^2}{\pi b}Official answer
  2. (2)2μoI2a3πb2\frac{2\mu_o I^2 a^3}{\pi b^2}
  3. (3)μoI2a32πb2\frac{\mu_o I^2 a^3}{2\pi b^2}
  4. (4)μoI2a22πb\frac{\mu_o I^2 a^2}{2\pi b}

Official answer

Option 1

NTA final key (Sep 2020).

Chapter
Moving Charges and Magnetism
Topic
Magnetic Dipole Moment
Idea tested
Torque on a dipole in uniform field

Same idea in other shifts

Asked 6× in all
  1. 4 Apr 2026, Shift 2 · Q49A circular coil of radius 2 cm and 125 turns carries a current of 1 A. The coil is placed in a uniform magnetic field of magnitude 0.4 T.…EasyNumerical value
  2. 8 Apr 2026, Shift 2 · Q39A current carrying circular loop of radius 2 cm with unit normal n^=k^+i^2\hat{n} = \frac{\hat{k} + \hat{i}}{\sqrt{2}} is placed in a magnetic…MediumSingle correct
  3. 31 Jan 2024, Shift 2 · Q42A uniform magnetic field of 2×10−32\times10^{-3} T acts along positive YY-direction. A rectangular loop of sides 20 cm and 10 cm with current…MediumSingle correct
  4. 26 Aug 2021, Shift 2 · Q29A coil in the shape of an equilateral triangle of side 10 cm lies in a vertical plane between the pole pieces of permanent magnet…MediumNumerical value
  5. 3 Sep 2020, Shift 2 · Q24A galvanometer coil has 500 turns and each turn has an average area of 3×10−43 \times 10^{-4} m2^2. If a torque of 1.5 Nm is required to keep…EasyNumerical value

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.