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Friday, 9 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 9 January 2020, Shift 2, Physics Q13

Question 13 of 75 in this shift, Physics question 13 of 25, Section A.

A small circular loop of conducting wire has radius aa and carries current II. It is placed in a uniform magnetic field BB perpendicular to its plane such that when rotated slightly about its diameter and released, it starts performing simple harmonic motion of time period TT. If the mass of the loop is mm then :
  1. (1)T=2mIBT = \sqrt{\frac{2m}{IB}}
  2. (2)T=πmIBT = \sqrt{\frac{\pi m}{IB}}
  3. (3)T=2πmIBT = \sqrt{\frac{2\pi m}{IB}}Official answer
  4. (4)T=πm2IBT = \sqrt{\frac{\pi m}{2IB}}

Official answer

Option 3

NTA final key (Jan 2020).

Chapter
Moving Charges and Magnetism
Topic
Magnetic Dipole Moment
Idea tested
Small Oscillations of a Magnetic Dipole

Same idea in other shifts

Asked 2× in all
  1. 2 Apr 2017 (offline) · Q18A magnetic needle of magnetic moment 6.7×10−2 Am26.7\times10^{-2}\ \mathrm{Am^2} and moment of inertia 7.5×10−6 kg m27.5\times10^{-6}\ \mathrm{kg\,m^2} is…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 42 of the 174 JEE Main shifts held from 2017 to 2026.