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Friday, 9 October

JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 3 August 2021, Shift 2, Physics Q14

Question 14 of 90 in this shift, Physics question 14 of 30, Section A.

Two concentric and coplanar circular coils have radius aa and b (≫a)b\ (\gg a) as shown in figure. Resistance of the inner coil is RR. Current in the outer coil is increased from 0 to ii, then total charge circulating the inner coil is

The figure, in words

Two concentric coplanar circular coils; small inner coil of radius a, large outer coil of radius b.
  1. (1)μ0iπa2R\frac{\mu_0 i\pi a}{2R}
  2. (2)μ0i2πa2R\frac{\mu_0 i^2\pi a}{2R}
  3. (3)μ0i2πa3R\frac{\mu_0 i^2\pi a}{3R}
  4. (4)μ0iπa22Rb\frac{\mu_0 i\pi a^2}{2Rb}Official answer

Official answer

Option 4

NTA final key.

Chapter
Electromagnetic Induction
Topic
Faraday's Law
Idea tested
Induced Charge Flow

Same idea in other shifts

Asked 3× in all
  1. 13 Apr 2023, Shift 2 · Q58An insulated copper wire of 100 turns is wrapped around a wooden cylindrical core of the cross-sectional area 24 cm224\ \mathrm{cm^2}. The two…EasyNumerical value
  2. 2 Apr 2017 (offline) · Q20In a coil of resistance 100 Ω100\ \Omega, a current is induced by changing the magnetic flux through it as shown in the figure. The magnitude…MediumSingle correctHas a figure

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. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.