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Saturday, 31 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 6 September 2020, Shift 2, Physics Q8

Question 8 of 75 in this shift, Physics question 8 of 25.

Three rods of identical cross-section and lengths are made of three different materials of thermal conductivity K1K_1, K2K_2 and K3K_3, 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∘100^\circC and the other at 0∘0^\circC (see figure). If the joints of the rod are at 70∘70^\circC and 20∘20^\circC in steady state and there is no loss of energy from the surface of the rod, the correct relationship between K1K_1, K2K_2 and K3K_3 is :

The figure, in words

Three rods in series labelled K1, K2, K3 left to right; left end at 100 C, right end at 0 C; joint between K1 and K2 at 70 C, joint between K2 and K3 at 20 C
  1. (1)K1>K2>K3K_1>K_2>K_3
  2. (2)K1<K2<K3K_1<K_2<K_3
  3. (3)K1:K2=5:2K_1:K_2=5:2, K1:K3=3:5K_1:K_3=3:5
  4. (4)K1:K3=2:3K_1:K_3=2:3, K2:K3=2:5K_2:K_3=2:5Official answer

Official answer

Option 4

NTA final key (Sep 2020).

Chapter
Thermal Properties of Matter
Topic
Heat Conduction
Idea tested
Slabs in Series

Same topic in other shifts

All Heat Conduction questions
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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.