Thermal Properties of Matter: JEE Main Previous Year Questions (2021-2026)

 Page 1


JEE Main Previous Year Questions (2021-2026): 
Thermal Properties of Matter 
 
(January 2026) 
 
Q1: Two wires A and B made of different materials of lengths 6.0 cm and 5.4 cm , 
respectively and area of cross sections 3.0 × 10
-5
 m
2
 and 4.5 × 10
-5
 m
2
 , respectively are 
stretched by the same magnitude under a given load. The ratio of the Young's modulus of 
A to that of B is x : 3. The value of x is 
(a) 2 
(b) 1 
(c) 4 
(d) 5 
Ans: (d) 
Sol:  
 
Young's Modulus is given by : 
 
Where: 
F is the applied force (load) 
L is the original length. 
A is the area of cross-section 
Page 2


JEE Main Previous Year Questions (2021-2026): 
Thermal Properties of Matter 
 
(January 2026) 
 
Q1: Two wires A and B made of different materials of lengths 6.0 cm and 5.4 cm , 
respectively and area of cross sections 3.0 × 10
-5
 m
2
 and 4.5 × 10
-5
 m
2
 , respectively are 
stretched by the same magnitude under a given load. The ratio of the Young's modulus of 
A to that of B is x : 3. The value of x is 
(a) 2 
(b) 1 
(c) 4 
(d) 5 
Ans: (d) 
Sol:  
 
Young's Modulus is given by : 
 
Where: 
F is the applied force (load) 
L is the original length. 
A is the area of cross-section 
?L is the change in length (stretching) According to question, both wires are stretched by the 
same magnitude (?L
A
 = ?L
B
) under the same given load (F
A
 = F
B
).  
Therefore, for both wires: 
 
Let Y
A
 and Y
B
 be the Young's moduli for wires A and B: 
 
The given values : 
 
So, the value of x is 5 . Hence, the correct option is (d). 
 
 
Q2: A cubical block of density ?
b
 = 600 kg / m
3
 floats in a liquid of density ?
e
 = 900 kg / m
3
. 
If the height of block is H = 8.0 cm then height of the submerged part is ____ cm.  
(a) 6.3  
(b) 4.3  
(c) 7.3  
(d) 5.3  
Ans: (d) 
Sol:  
When an object floats in a liquid, the weight of the object is exactly balanced by the buoyant 
force (up thrust) exerted by the liquid. 
Page 3


JEE Main Previous Year Questions (2021-2026): 
Thermal Properties of Matter 
 
(January 2026) 
 
Q1: Two wires A and B made of different materials of lengths 6.0 cm and 5.4 cm , 
respectively and area of cross sections 3.0 × 10
-5
 m
2
 and 4.5 × 10
-5
 m
2
 , respectively are 
stretched by the same magnitude under a given load. The ratio of the Young's modulus of 
A to that of B is x : 3. The value of x is 
(a) 2 
(b) 1 
(c) 4 
(d) 5 
Ans: (d) 
Sol:  
 
Young's Modulus is given by : 
 
Where: 
F is the applied force (load) 
L is the original length. 
A is the area of cross-section 
?L is the change in length (stretching) According to question, both wires are stretched by the 
same magnitude (?L
A
 = ?L
B
) under the same given load (F
A
 = F
B
).  
Therefore, for both wires: 
 
Let Y
A
 and Y
B
 be the Young's moduli for wires A and B: 
 
The given values : 
 
So, the value of x is 5 . Hence, the correct option is (d). 
 
 
Q2: A cubical block of density ?
b
 = 600 kg / m
3
 floats in a liquid of density ?
e
 = 900 kg / m
3
. 
If the height of block is H = 8.0 cm then height of the submerged part is ____ cm.  
(a) 6.3  
(b) 4.3  
(c) 7.3  
(d) 5.3  
Ans: (d) 
Sol:  
When an object floats in a liquid, the weight of the object is exactly balanced by the buoyant 
force (up thrust) exerted by the liquid. 
 
Weight of block is  
Buoyant force (F
B
) acting on a submerged body is equal to the weight of displaced liquid, 
 
For flotation : 
 
For a cubical block with a uniform cross-sectional area (A): 
Total Volume = V
total 
= AH 
Submerged Volume V
submerged
 = Ah  (where h is the submerged height) 
 
Putting the given values, 
Page 4


JEE Main Previous Year Questions (2021-2026): 
Thermal Properties of Matter 
 
(January 2026) 
 
Q1: Two wires A and B made of different materials of lengths 6.0 cm and 5.4 cm , 
respectively and area of cross sections 3.0 × 10
-5
 m
2
 and 4.5 × 10
-5
 m
2
 , respectively are 
stretched by the same magnitude under a given load. The ratio of the Young's modulus of 
A to that of B is x : 3. The value of x is 
(a) 2 
(b) 1 
(c) 4 
(d) 5 
Ans: (d) 
Sol:  
 
Young's Modulus is given by : 
 
Where: 
F is the applied force (load) 
L is the original length. 
A is the area of cross-section 
?L is the change in length (stretching) According to question, both wires are stretched by the 
same magnitude (?L
A
 = ?L
B
) under the same given load (F
A
 = F
B
).  
Therefore, for both wires: 
 
Let Y
A
 and Y
B
 be the Young's moduli for wires A and B: 
 
The given values : 
 
So, the value of x is 5 . Hence, the correct option is (d). 
 
 
Q2: A cubical block of density ?
b
 = 600 kg / m
3
 floats in a liquid of density ?
e
 = 900 kg / m
3
. 
If the height of block is H = 8.0 cm then height of the submerged part is ____ cm.  
(a) 6.3  
(b) 4.3  
(c) 7.3  
(d) 5.3  
Ans: (d) 
Sol:  
When an object floats in a liquid, the weight of the object is exactly balanced by the buoyant 
force (up thrust) exerted by the liquid. 
 
Weight of block is  
Buoyant force (F
B
) acting on a submerged body is equal to the weight of displaced liquid, 
 
For flotation : 
 
For a cubical block with a uniform cross-sectional area (A): 
Total Volume = V
total 
= AH 
Submerged Volume V
submerged
 = Ah  (where h is the submerged height) 
 
Putting the given values, 
 
Therefore, the height of the submerged part of the block is approximately 5.3 cm. 
Hence, the correct option is (d). 
 
Q3: A brass wire of length 2 m and radius 1 mm at 27
°
C is held taut between two rigid 
supports. Initially it was cooled to a temperature of - 43
°
C creating a tension T in the 
wire. The temperature to which the wire has to be cooled in order to increase the tension 
in it to 1.4 T, is _ _ _ _ °C.  
(a) -71  
(b) -80  
(c)  -65  
(d) -86  
Ans: (a) 
Sol:  
A metal rod of original length L that is free to move. If we heat this rod by a temperature 
difference ?T, it will naturally expand.  
The change in length (?L) is given by the law of linear thermal expansion: 
 
Where a = Coefficient of Linear Expansion  
When a wire fixed at both ends is cooled, it contracts. Since the supports are rigid, they prevent 
this contraction, creating a tension in the wire. 
 
According to Hooke's Law, Stress is proportional to Strain within the elastic limit. The constant of 
proportionality is Young's Modulus (Y). 
 
Page 5


JEE Main Previous Year Questions (2021-2026): 
Thermal Properties of Matter 
 
(January 2026) 
 
Q1: Two wires A and B made of different materials of lengths 6.0 cm and 5.4 cm , 
respectively and area of cross sections 3.0 × 10
-5
 m
2
 and 4.5 × 10
-5
 m
2
 , respectively are 
stretched by the same magnitude under a given load. The ratio of the Young's modulus of 
A to that of B is x : 3. The value of x is 
(a) 2 
(b) 1 
(c) 4 
(d) 5 
Ans: (d) 
Sol:  
 
Young's Modulus is given by : 
 
Where: 
F is the applied force (load) 
L is the original length. 
A is the area of cross-section 
?L is the change in length (stretching) According to question, both wires are stretched by the 
same magnitude (?L
A
 = ?L
B
) under the same given load (F
A
 = F
B
).  
Therefore, for both wires: 
 
Let Y
A
 and Y
B
 be the Young's moduli for wires A and B: 
 
The given values : 
 
So, the value of x is 5 . Hence, the correct option is (d). 
 
 
Q2: A cubical block of density ?
b
 = 600 kg / m
3
 floats in a liquid of density ?
e
 = 900 kg / m
3
. 
If the height of block is H = 8.0 cm then height of the submerged part is ____ cm.  
(a) 6.3  
(b) 4.3  
(c) 7.3  
(d) 5.3  
Ans: (d) 
Sol:  
When an object floats in a liquid, the weight of the object is exactly balanced by the buoyant 
force (up thrust) exerted by the liquid. 
 
Weight of block is  
Buoyant force (F
B
) acting on a submerged body is equal to the weight of displaced liquid, 
 
For flotation : 
 
For a cubical block with a uniform cross-sectional area (A): 
Total Volume = V
total 
= AH 
Submerged Volume V
submerged
 = Ah  (where h is the submerged height) 
 
Putting the given values, 
 
Therefore, the height of the submerged part of the block is approximately 5.3 cm. 
Hence, the correct option is (d). 
 
Q3: A brass wire of length 2 m and radius 1 mm at 27
°
C is held taut between two rigid 
supports. Initially it was cooled to a temperature of - 43
°
C creating a tension T in the 
wire. The temperature to which the wire has to be cooled in order to increase the tension 
in it to 1.4 T, is _ _ _ _ °C.  
(a) -71  
(b) -80  
(c)  -65  
(d) -86  
Ans: (a) 
Sol:  
A metal rod of original length L that is free to move. If we heat this rod by a temperature 
difference ?T, it will naturally expand.  
The change in length (?L) is given by the law of linear thermal expansion: 
 
Where a = Coefficient of Linear Expansion  
When a wire fixed at both ends is cooled, it contracts. Since the supports are rigid, they prevent 
this contraction, creating a tension in the wire. 
 
According to Hooke's Law, Stress is proportional to Strain within the elastic limit. The constant of 
proportionality is Young's Modulus (Y). 
 
Stress is defined as Force (F) per unit Area (A). 
 
Let the new final temperature be t
2
.