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Three rods of identical cross-section and length are made of three different materials of thermal conductivity K_1,K_2 and K_3, respectively. They…

JEE Main 2020 — Physics Thermodynamics

2020mcqmedium

Three rods of identical cross-section and length are made of three different materials of thermal conductivity K1,K2{K}_{1},{K}_{2}K1​,K2​ and K3{K}_{3}K3​, respectively. They are joined together at their ends to make a long rod (see figure). One end of the long rod is maintained at 100∘C100^{\circ}C100∘C and the other at 0∘C0^{\circ}C0∘C (see figure). If the joints of the rod are at 70∘C70^{\circ}C70∘C and 20∘C20^{\circ}C20∘C in steady and there is no loss of energy from the surface of the rod, the correct relationship between K1,K2{K}_{1},{K}_{2}K1​,K2​ and K3{K}_{3}K3​ is :

JEE Main 2020 Physics, Thermal Properties of Matter — question figure

Official previous-year question

Held on 6 Sept 2020 · Verified 6 Jul 2026.

Options

  1. A

    K1:K3=2:3{K}_{1}:{K}_{3}=2:3K1​:K3​=2:3,

    K2:K3=2:5{K}_{2}:{K}_{3}=2:5K2​:K3​=2:5

  2. B

    K1<K2<K3{K}_{1}<{K}_{2}<{K}_{3}K1​<K2​<K3​

  3. C

    K1:K2=5:2{K}_{1}:{K}_{2}=5:2K1​:K2​=5:2,

    K1:K3=3:5{K}_{1}:{K}_{3}=3:5K1​:K3​=3:5

  4. D

    K1>K2>K3{K}_{1}>{K}_{2}>{K}_{3}K1​>K2​>K3​

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