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JEE Main 2021 · PhysicsNumerical answerNumerical valueMediumMulti-step

JEE Main 25 July 2021, Shift 1, Physics Q26

Question 26 of 90 in this shift, Physics question 26 of 30, Section B.

A circular conducting coil of radius 1 m is being heated by the change of magnetic field B⃗\vec{B} passing perpendicular to the plane in which the coil is laid. The resistance of the coil is 2 μΩ2\ \mu\Omega. The magnetic field is slowly switched off such that its magnitude changes in time as B=4π×10−3 T(1−t100)B=\frac{4}{\pi}\times10^{-3}\,\mathrm{T}\left(1-\frac{t}{100}\right) The energy dissipated by the coil before the magnetic field is switched off completely is E=_______ mJ.

Official answer

80

NTA final key.

Chapter
Electromagnetic Induction
Topic
Faraday's Law
Idea tested
Faraday's Law Magnitude

Same idea in other shifts

Asked 15× in all
  1. 5 Apr 2026, Shift 2 · Q50A circular loop of radius 20 cm and resistance 2 Ω\Omega is placed in a time varying magnetic field B⃗=(2t2+2t+3) T\vec{B}=(2t^2+2t+3)\ \mathrm{T}. At…EasyNumerical value
  2. 6 Apr 2026, Shift 2 · Q39A square loop of side 2 cm is placed in a time varying magnetic field with magnitude as B=0.4sin⁡(300t)B=0.4\sin(300t) Tesla. The normal to the plane…MediumSingle correct
  3. 29 Jan 2024, Shift 1 · Q58A square loop of side 10 cm and resistance 0.7 Ω0.7\,\Omega is placed vertically in east-west plane. A uniform magnetic field of 0.20 T0.20\ T is…EasyNumerical value
  4. 31 Jan 2024, Shift 2 · Q58The magnetic flux ϕ\phi (in weber) linked with a closed circuit of resistance 8 Ω8\ \Omega varies with time (in seconds) as…EasyNumerical value
  5. 11 Apr 2023, Shift 1 · Q53The magnetic field B crossing normally a square metallic plate of area 4 m2^2 is changing with time as shown in figure. The magnitude of…EasyNumerical valueHas a figure
  6. 12 Apr 2023, Shift 1 · Q58A conducting circular loop is placed in a uniform magnetic field of 0.4 T with its plane perpendicular to the field. Somehow, the radius…MediumNumerical value
  7. 25 Jul 2022, Shift 2 · Q60Magnetic flux (in weber) in a closed circuit of resistance 20 Ω\Omega varies with time t(s) as ϕ\phi = 8t2^{2} - 9t + 5. The magnitude…EasyNumerical value
  8. 26 Jul 2022, Shift 2 · Q58In a coil of resistance 8 Ω\Omega,the magnetic flux due to an external magnetic field varies with time as…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.