JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 26 August 2021, Shift 1, Physics Q9

Question 9 of 90 in this shift, Physics question 9 of 30, Section A.

An 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 it. If this coil is joined across an ideal battery, find the time constant of the circuit in seconds :

(1)0.2Official answer
(2)0.4
(3)0.8
(4)0.125

Official answer

Option 1

NTA final key.

Chapter: Electromagnetic Induction
Topic: Inductance
Idea tested: Energy Stored in Inductors

Same idea in other shifts

Asked 7× in all

5 Apr 2026, Shift 1 · Q50In the given circuit below inductance values of $L_1$ , $L_2$ and $L_3$ are same. The magnetic energy stored in the entire circuit is…MediumNumerical valueHas a figure
11 Apr 2023, Shift 2 · Q57A coil has an inductance of $2\mathrm{H}$ and resistance of $4\ \Omega$ . A $10\ \mathrm{V}$ is applied across the coil. The energy stored…EasyNumerical value
25 Jun 2022, Shift 1 · Q59The current in a coil of self inductance 2.0 H is increasing according to I=2 sin( $t^2$ ) A. The amount of energy spent during the period…MediumNumerical value
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
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
4 Sep 2020, Shift 2 · Q15A series L-R circuit is connected to a battery of emf V. If the circuit is switched on at $t=0$ , then the time at which the energy stored…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. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.