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Saturday, 31 October

JEE Main 2022 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 24 June 2022, Shift 1, Physics Q50

Question 50 of 90 in this shift, Physics question 20 of 30, Section A.

Two metallic blocks M1M_1 and M2M_2 of same area of cross-section are connected to each other (as shown in figure). If the thermal conductivity of M2M_2 is K then the thermal conductivity of M1M_1 will be : [Assume steady state heat conduction]

The figure, in words

Two blocks M1 (length 16 cm) and M2 (length 8 cm) joined end to end; left end of M1 at 100°C, junction at 80°C, right end of M2 at 0°C.
  1. (1)10 K
  2. (2)8 KOfficial answer
  3. (3)12.5 K
  4. (4)2 K

Official answer

Option 2

NTA final key (2022 Session 1).

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

Same idea in other shifts

Asked 6× in all
  1. 7 Apr 2025, Shift 2 · Q47Two cylindrical rods A and B made of different materials, are joined in a straight line. The ratios of lengths, radii and thermal…MediumNumerical value
  2. 13 Apr 2023, Shift 2 · Q53Two plates A and B have thermal conductivities 84 Wm−1K−184\ \mathrm{Wm^{-1}K^{-1}} and 126 Wm−1K−1126\ \mathrm{Wm^{-1}K^{-1}} respectively. They have same…EasyNumerical value
  3. 27 Jul 2022, Shift 1 · Q37If K1K_1 and K2K_2 are the thermal conductivities, L1L_1 and L2L_2 are the lengths and A1A_1 and A2A_2 are the cross sectional areas of…MediumSingle correctHas a figure
  4. 27 Aug 2021, Shift 1 · Q30A rod CD of thermal resistance 10.0 KW−1^{-1} is joined at the middle of an identical rod AB as shown in figure. The ends A, B and D are…MediumNumerical valueHas a figure
  5. 26 Feb 2021, Shift 1 · Q9The 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…EasyDiagram basedHas 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 108 of the 174 JEE Main shifts held from 2017 to 2026.