JEE Main · Physics · Thermal Properties of Matter

Heat Conduction: JEE Main previous year questions

Name: Heat Conduction: JEE Main previous year questions
Creator: Lumi

11 questions in the 108 JEE Main shifts Lumi analysed, in 5 of 8 years. Pattern: Asked most years. 1 came in 2024–26. Here is how it is asked and which ideas come back.

Questions: 11; in 11 of 108 shifts
Years asked: 5/8; last asked 2025
Chance in a shift: 13%; calibrated model, how we compute it
Weighted estimate: 0.1; model; history: 0.1 a shift on average, typically 0.0–0.1

Key findings

01
Asked in 5 of 8 years with analysed shifts and in 11 of 108 shifts: 11 questions, #174 of 196 topics. The years that asked it were 1.2 apart on average. Last asked in 2025.
02
64% of its questions since 2020 tested an idea no earlier year had asked; 3 repeated an idea from the year before.
03
The most repeated idea is Junction Temperature, asked 6 times in 6 shifts (2021, 2022, 2023, 2025), most often as “interface temperature of two rods”.
04
JEE Main has asked 6 of the 56 ideas in this topic; 50 have never been asked, directly or inside another question.
05
Mostly asked as single correct (55%); 36% need a numerical answer, 36% are easy and 0% hard.
06
The skill tested most is calculation (64%), then multi-step (27%).

Questions a shift, year by year

Out of the 25 Physics questions in a shift. Years differ in how many shifts Lumi analysed, so each year is scaled to one shift.

Raw count: 2017: 0 in 1 shift · 2020: 1 in 12 shifts · 2021: 4 in 24 shifts · 2022: 4 in 24 shifts · 2023: 1 in 12 shifts · 2024: 0 in 18 shifts · 2025: 1 in 8 shifts · 2026: 0 in 9 shifts.

Up to 2023: 0.1; a shift, of 25
Since 2024: 0.0; 0.0
Usual gap: 1.2 yrs; between years asking it
Shifts with it: 11/108; 10% of analysed shifts

How it is asked

Difficulty, format and skill

Across all 11 questions on Heat Conduction since 2017.

Difficulty

QUESTIONS

Easy4 · 36%
Medium7 · 64%
Hard0 · 0%

Format

Single correct · 6 Q55%
Numerical value · 4 Q36%
Diagram based · 1 Q9%

Skill tested

Calculation · 7 Q64%
Multi-step · 3 Q27%
Application · 1 Q9%

Repeats

New idea, or one asked before?

Each column is a year. Blue questions tested an idea no earlier year had asked; navy ones went back to an idea from an earlier year. 2017 is the first year, so everything in it counts as new. Heights are question counts, and Lumi analysed 1 to 24 shifts a year, so compare the split inside a column rather than heights across years.

’17’20’21’22’23’24’25’26

Idea asked for the first time
Idea asked in an earlier year

Coverage of the topic

JEE Main has asked 6 of the 56 ideas in this topic. 50 have never been asked yet.

650

Asked directly6 · 11%
Touched inside another question0 · 0%
Never asked50 · 89%

Ideas come from Lumi’s JEE syllabus map. A never-asked idea is not a safe skip: across all of JEE Main, 22% of questions since 2024 tested an idea no earlier year had asked.

Drill down

Idea, year, question

Every idea JEE Main tested in this topic, with its eight years. Open one to read the questions.

ideaAskedShareYears’17’20’21’22’23’24’25’26

OpenRepeated6 · 55%55%4/822
- 7 Apr ’25 S2 · Q47
  Two cylindrical rods A and B made of different materials, are joined in a straight line. The ratios of lengths, radii and thermal…
  mediumNumerical value
- 13 Apr ’23 S2 · Q53
  Two plates A and B have thermal conductivities $84\ \mathrm{Wm^{-1}K^{-1}}$ and $126\ \mathrm{Wm^{-1}K^{-1}}$ respectively. They have same…
  easyNumerical valueAsked the year before
- 27 Jul ’22 S1 · Q37
  If $K_1$ and $K_2$ are the thermal conductivities, $L_1$ and $L_2$ are the lengths and $A_1$ and $A_2$ are the cross sectional areas of…
  mediumSingle correctAsked the year before
- 24 Jun ’22 S1 · Q50
  Two metallic blocks $M_1$ and $M_2$ of same area of cross-section are connected to each other (as shown in figure). If the thermal…
  mediumSingle correctAsked the year before
- 27 Aug ’21 S1 · Q30
  A rod CD of thermal resistance 10.0 KW $^{-1}$ is joined at the middle of an identical rod AB as shown in figure. The ends A, B and D are…
  mediumNumerical valueNew idea
- 26 Feb ’21 S1 · Q9
  The temperature $\theta$ at the junction of two insulating sheets, having thermal resistances $\mathrm{R_1}$ and $\mathrm{R_2}$ as well as…
  easyDiagram basedNew idea
Open1 · 9%9%1/8
Open1 · 9%9%1/8
Open1 · 9%9%1/8
Open1 · 9%9%1/8
Open1 · 9%9%1/8

Squares are the 8 years with analysed shifts, 2017 to 2026. A number is the questions that year when there is more than one; the shade is scaled to one shift, so a year with more analysed shifts (1 to 24 a year) does not look darker. Share is of the level above.

Ideas

Every idea inside this topic

6 different ideas were tested; 1 came more than once.

Junction Temperature6×
interface temperature of two rods
Numerical value · 6 shifts · 3 numerical
Equivalent Thermal Conductivity (Series)1×
equivalent conductivity of compound plate
Numerical value · 1 shift · 1 numerical
Fourier's Law of Conduction1×
rate of melting from conduction through box walls
Single correct · 1 shift
Equivalent Thermal Conductivity in Series1×
effective conductivity of two rods in series
Single correct · 1 shift
Radial Conduction in Spherical Shells1×
radial heat flow through spherical shells
Single correct · 1 shift
Slabs in Series1×
relation among conductivities from junction temperatures
Single correct · 1 shift

Idea	Times	Shifts	Format	Numerical
Junction Temperatureinterface temperature of two rods	6	6	Numerical valueCalculation	3
Equivalent Thermal Conductivity (Series)equivalent conductivity of compound plate	1	1	Numerical valueCalculation	1
Fourier's Law of Conductionrate of melting from conduction through box walls	1	1	Single correctMulti-step	–
Equivalent Thermal Conductivity in Serieseffective conductivity of two rods in series	1	1	Single correctCalculation	–
Radial Conduction in Spherical Shellsradial heat flow through spherical shells	1	1	Single correctCalculation	–
Slabs in Seriesrelation among conductivities from junction temperatures	1	1	Single correctMulti-step	–

Times and shifts count every analysed shift. Across JEE Main, 78% of questions since 2024 went back to an idea an earlier year had asked; the rest were new. All repeated ideas

Every question

Heat Conduction questions, year by year

The opening words of each question as it appeared in the official paper, with the idea it tested. Open one for its options and the official answer.

Questions from the official JEE Main Paper 1 shifts published by NTA (CBSE for 2017). Questions NTA dropped are left out. Topic and idea tags, counts and notes are Lumi’s.

Key findings

Questions a shift, year by year

Difficulty, format and skill

Difficulty

Format

Skill tested

New idea, or one asked before?

Coverage of the topic

Idea, year, question

Every idea inside this topic

Heat Conduction questions, year by year

JEE Main 20251 question in 1 shift

JEE Main 20231 question in 1 shift

JEE Main 20224 questions in 4 shifts

JEE Main 20214 questions in 4 shifts

JEE Main 20201 question in 1 shift

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