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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 31 August 2021, Shift 2, Physics Q4

Question 4 of 90 in this shift, Physics question 4 of 30, Section A.

Two thin metallic spherical shells of radii r1r_1 and r2r_2 (r1<r2r_1 < r_2) are placed with their centres coinciding. A material of thermal conductivity K is filled in the space between the shells. The inner shell is maintained at temperature θ1\theta_1 and the outer shell at temperature θ2(θ1<θ2)\theta_2(\theta_1 < \theta_2). The rate at which heat flows radially through the material is :
  1. (1)4πKr1r2(θ2−θ1)r2−r1\frac{4\pi K r_1 r_2(\theta_2-\theta_1)}{r_2-r_1}Official answer
  2. (2)K(θ2−θ1)(r2−r1)4πr1r2\frac{K(\theta_2-\theta_1)(r_2-r_1)}{4\pi r_1 r_2}
  3. (3)K(θ2−θ1)r2−r1\frac{K(\theta_2-\theta_1)}{r_2-r_1}
  4. (4)πr1r2(θ2−θ1)r2−r1\frac{\pi r_1 r_2(\theta_2-\theta_1)}{r_2-r_1}

Official answer

Option 1

NTA final key.

Chapter
Thermal Properties of Matter
Topic
Heat Conduction
Idea tested
Radial Conduction in Spherical Shells

Same topic in other shifts

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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.