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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 4 September 2020, Shift 2, Physics Q15

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

A series L-R circuit is connected to a battery of emf V. If the circuit is switched on at t=0t=0, then the time at which the energy stored in the inductor reaches (1n)\left(\frac{1}{n}\right) times of its maximum value, is :
  1. (1)LRln⁡(n−1n)\frac{L}{R}\ln\left(\frac{\sqrt{n}-1}{\sqrt{n}}\right)
  2. (2)LRln⁡(n+1n−1)\frac{L}{R}\ln\left(\frac{\sqrt{n}+1}{\sqrt{n}-1}\right)
  3. (3)LRln⁡(nn−1)\frac{L}{R}\ln\left(\frac{\sqrt{n}}{\sqrt{n}-1}\right)Official answer
  4. (4)LRln⁡(nn+1)\frac{L}{R}\ln\left(\frac{\sqrt{n}}{\sqrt{n}+1}\right)

Official answer

Option 3

NTA final key (Sep 2020).

Chapter
Electromagnetic Induction
Topic
Inductance
Idea tested
Energy Stored in Inductors

Same idea in other shifts

Asked 7× in all
  1. 5 Apr 2026, Shift 1 · Q50In the given circuit below inductance values of L1L_1, L2L_2 and L3L_3 are same. The magnetic energy stored in the entire circuit is…MediumNumerical valueHas a figure
  2. 11 Apr 2023, Shift 2 · Q57A coil has an inductance of 2H2\mathrm{H} and resistance of 4 Ω4\ \Omega. A 10 V10\ \mathrm{V} is applied across the coil. The energy stored…EasyNumerical value
  3. 25 Jun 2022, Shift 1 · Q59The current in a coil of self inductance 2.0 H is increasing according to I=2 sin(t2t^2) A. The amount of energy spent during the period…MediumNumerical value
  4. 3 Aug 2021, Shift 1 · Q24An inductor coil stores 32 J of magnetic field energy and dissipates energy as heat at the rate of 64 W when a current of 8 A is passed…MediumNumerical value
  5. 26 Aug 2021, Shift 1 · Q9An inductor coil stores 64 J of magnetic field energy and dissipates energy at the rate of 640 W when a current of 8 A is passed through…MediumSingle correct
  6. 25 Feb 2021, Shift 1 · Q23A coil of inductance 2 H having negligible resistance is connected to a source of supply whose voltage is given by V=3t volt. (where t is…MediumNumerical 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.