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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedEasyApplication

JEE Main 26 February 2021, Shift 1, Physics Q9

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

The temperature θ\theta at the junction of two insulating sheets, having thermal resistances R1\mathrm{R_1} and R2\mathrm{R_2} as well as top and bottom temperatures θ1\theta_1 and θ2\theta_2 (as shown in figure) is given by :

The figure, in words

Drawn: a horizontal rectangular slab made of two stacked layers. The upper layer (vertical-line hatching) is labelled R_2 and the lower layer (dotted shading) is labelled R_1. On the right side, labels from top to bottom: θ2\theta_2 (at the top edge), θ\theta (at the junction between the layers), θ1\theta_1 (at the bottom edge).
  1. (1)θ1R2+θ2R1R1+R2\frac{\theta_1\mathrm{R_2}+\theta_2\mathrm{R_1}}{\mathrm{R_1}+\mathrm{R_2}}Official answer
  2. (2)θ1R1+θ2R2R1+R2\frac{\theta_1\mathrm{R_1}+\theta_2\mathrm{R_2}}{\mathrm{R_1}+\mathrm{R_2}}
  3. (3)θ1R2−θ2R1R2−R1\frac{\theta_1\mathrm{R_2}-\theta_2\mathrm{R_1}}{\mathrm{R_2}-\mathrm{R_1}}
  4. (4)θ2R2−θ1R1R2−R1\frac{\theta_2\mathrm{R_2}-\theta_1\mathrm{R_1}}{\mathrm{R_2}-\mathrm{R_1}}

Official answer

Option 1

NTA final key.

Chapter
Thermal Properties of Matter
Topic
Heat Conduction
Idea tested
Junction Temperature

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Asked 6× in all
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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. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.