Page 1
JEE Main Previous Year Questions
(2025): Thermodynamics
Q1:Three conductors of same length having thermal conductivity ?? ?? , ?? ?? and ?? ?? are
connected as shown in figure.
Area of cross sections of 1
st
and 2
nd
3
rd
conductor it is double of the 1
st
conductor. The
temperatures are given in the figure. In steady state condition, the value of ?? is ____
°
C. (Given :
k
1
= 60Js
-1
m
-1
K
-1
, k
2
= 120 Js
-1
m
-1
K
-1
, k
3
= 135 Js
-1
m
-1
K
-1
) conductor are same
and for
Ans: 40
?? 1
=
2?? ?? 1
??
(As ?? 1
= ?? 2
= ?? 3
= ??
?? 1
= ?? 2
= ?? /2
?? 3
= ?? )
?? 2
=
2?? ?? 2
??
Page 2
JEE Main Previous Year Questions
(2025): Thermodynamics
Q1:Three conductors of same length having thermal conductivity ?? ?? , ?? ?? and ?? ?? are
connected as shown in figure.
Area of cross sections of 1
st
and 2
nd
3
rd
conductor it is double of the 1
st
conductor. The
temperatures are given in the figure. In steady state condition, the value of ?? is ____
°
C. (Given :
k
1
= 60Js
-1
m
-1
K
-1
, k
2
= 120 Js
-1
m
-1
K
-1
, k
3
= 135 Js
-1
m
-1
K
-1
) conductor are same
and for
Ans: 40
?? 1
=
2?? ?? 1
??
(As ?? 1
= ?? 2
= ?? 3
= ??
?? 1
= ?? 2
= ?? /2
?? 3
= ?? )
?? 2
=
2?? ?? 2
??
?? 3
=
?? ?? 3
??
?? 1
+ ?? 2
= ?? 3
?
100- ?? 2?? ?? 1
?? +
100- ?? 2?? ?? 2
?? =
?? - 0
?? ?? 3
??
?
100- ?? 2
( ?? 1
+ ?? 2
) = ?? 3
??
? 50( ?? 1
+ ?? 2
)= ?? [?? 3
+
?? 1
+ ?? 2
2
]
? 50( 60 + 120 ) = ?? [135+
60 + 120
2
]
? 50 × 80 = ?? ( 135+ 90)
? ?? =
50 × 180
225
? ?? = 40
°
??
Q2: An ideal gas initially at ?? °
?? temperature, is compressed suddenly to one fourth of
its volume. If the ratio of specific heat at constant pressure to that at constant volume
is ?? /?? , the change in temperature due to the thermodynamic process is ____ K.
Ans: 273
Solution:
We're given an ideal gas initially at ?? ?? = 0
°
C = 273 K. The gas is suddenly compressed to one-
fourth of its initial volume, and we are told that
?? =
?? ?? ?? ?? =
3
2
.
For an adiabatic process (one in which there is no heat exchange), if the process were reversible,
the relation between the temperature and volume would be
?? ?? ?? -1
= constant.
Even though the compression is "sudden" (and hence irreversible), the final equilibrium state of
the gas is uniquely determined by its internal energy (which is a state function). That allows us
to use the adiabatic relation between the initial and final states.
Here are the steps:
Write the adiabatic relation between the initial and final states:
?? ?? ?? ?? ?? -1
= ?? ?? ?? ?? ?? -1
.
Since the gas is compressed to one-fourth of its volume, we have
?? ?? =
1
4
?? ?? .
Substitute this into the adiabatic relation:
273 ?? ?? ?? -1
= ?? ?? (
1
4
?? ?? )
?? -1
.
With ?? =
3
2
,
?? - 1 =
3
2
- 1 =
1
2
.
So the relation becomes:
Page 3
JEE Main Previous Year Questions
(2025): Thermodynamics
Q1:Three conductors of same length having thermal conductivity ?? ?? , ?? ?? and ?? ?? are
connected as shown in figure.
Area of cross sections of 1
st
and 2
nd
3
rd
conductor it is double of the 1
st
conductor. The
temperatures are given in the figure. In steady state condition, the value of ?? is ____
°
C. (Given :
k
1
= 60Js
-1
m
-1
K
-1
, k
2
= 120 Js
-1
m
-1
K
-1
, k
3
= 135 Js
-1
m
-1
K
-1
) conductor are same
and for
Ans: 40
?? 1
=
2?? ?? 1
??
(As ?? 1
= ?? 2
= ?? 3
= ??
?? 1
= ?? 2
= ?? /2
?? 3
= ?? )
?? 2
=
2?? ?? 2
??
?? 3
=
?? ?? 3
??
?? 1
+ ?? 2
= ?? 3
?
100- ?? 2?? ?? 1
?? +
100- ?? 2?? ?? 2
?? =
?? - 0
?? ?? 3
??
?
100- ?? 2
( ?? 1
+ ?? 2
) = ?? 3
??
? 50( ?? 1
+ ?? 2
)= ?? [?? 3
+
?? 1
+ ?? 2
2
]
? 50( 60 + 120 ) = ?? [135+
60 + 120
2
]
? 50 × 80 = ?? ( 135+ 90)
? ?? =
50 × 180
225
? ?? = 40
°
??
Q2: An ideal gas initially at ?? °
?? temperature, is compressed suddenly to one fourth of
its volume. If the ratio of specific heat at constant pressure to that at constant volume
is ?? /?? , the change in temperature due to the thermodynamic process is ____ K.
Ans: 273
Solution:
We're given an ideal gas initially at ?? ?? = 0
°
C = 273 K. The gas is suddenly compressed to one-
fourth of its initial volume, and we are told that
?? =
?? ?? ?? ?? =
3
2
.
For an adiabatic process (one in which there is no heat exchange), if the process were reversible,
the relation between the temperature and volume would be
?? ?? ?? -1
= constant.
Even though the compression is "sudden" (and hence irreversible), the final equilibrium state of
the gas is uniquely determined by its internal energy (which is a state function). That allows us
to use the adiabatic relation between the initial and final states.
Here are the steps:
Write the adiabatic relation between the initial and final states:
?? ?? ?? ?? ?? -1
= ?? ?? ?? ?? ?? -1
.
Since the gas is compressed to one-fourth of its volume, we have
?? ?? =
1
4
?? ?? .
Substitute this into the adiabatic relation:
273 ?? ?? ?? -1
= ?? ?? (
1
4
?? ?? )
?? -1
.
With ?? =
3
2
,
?? - 1 =
3
2
- 1 =
1
2
.
So the relation becomes:
273 ?? ?? 1/2
= ?? ?? (
1
4
)
1/2
?? ?? 1/2
.
Cancel the common factor ?? ?? 1/2
(provided it is nonzero) and simplify:
273 = ?? ?? (
1
2
).
Now solve for the final temperature ?? ?? :
?? ?? = 273× 2 = 546 K.
The change in temperature is then:
??? = ?? ?? - ?? ?? = 546 - 273 = 273 K.
So, the change in temperature due to the thermodynamic process is 273 K .
Q3: The temperature of 1 mole of an ideal monoatomic gas is increased by ????
°
?? at
constant pressure. The total heat added and change in internal energy are ?? ?? and ?? ?? ,
respectively. If
?? ?? ?? ?? =
?? ?? then the value of ?? is ____ .
JEE Main 2025 (Online) 24th January Morning Shift
Ans: 15
Solution:
?? = ?? ?? ?? ??? and ??? = ?? ?? ?? ???
For a monoatomic ideal gas, the molar specific heats are given by:
?? ?? =
3
2
?? and ?? ?? = ?? ?? + ?? =
5
2
??
Thus, the ratio of the heat added to the change in internal energy is:
?? ??? =
?? ?? ?? ?? =
5
2
?? 3
2
?? =
5
3
Given that:
?? 1
?? 2
=
?? 9
We equate the two ratios:
5
3
=
?? 9
Multiplying both sides by 9 :
?? =
5
3
× 9 = 15
Thus, the value of ?? is ???? .
Q4: A container of fixed volume contains a gas at ????
°
?? . To double the pressure of the
gas, the temperature of gas should be raised to ____
°
?? .
JEE Main 2025 (Online) 29th January Morning Shift
Ans: 327
Page 4
JEE Main Previous Year Questions
(2025): Thermodynamics
Q1:Three conductors of same length having thermal conductivity ?? ?? , ?? ?? and ?? ?? are
connected as shown in figure.
Area of cross sections of 1
st
and 2
nd
3
rd
conductor it is double of the 1
st
conductor. The
temperatures are given in the figure. In steady state condition, the value of ?? is ____
°
C. (Given :
k
1
= 60Js
-1
m
-1
K
-1
, k
2
= 120 Js
-1
m
-1
K
-1
, k
3
= 135 Js
-1
m
-1
K
-1
) conductor are same
and for
Ans: 40
?? 1
=
2?? ?? 1
??
(As ?? 1
= ?? 2
= ?? 3
= ??
?? 1
= ?? 2
= ?? /2
?? 3
= ?? )
?? 2
=
2?? ?? 2
??
?? 3
=
?? ?? 3
??
?? 1
+ ?? 2
= ?? 3
?
100- ?? 2?? ?? 1
?? +
100- ?? 2?? ?? 2
?? =
?? - 0
?? ?? 3
??
?
100- ?? 2
( ?? 1
+ ?? 2
) = ?? 3
??
? 50( ?? 1
+ ?? 2
)= ?? [?? 3
+
?? 1
+ ?? 2
2
]
? 50( 60 + 120 ) = ?? [135+
60 + 120
2
]
? 50 × 80 = ?? ( 135+ 90)
? ?? =
50 × 180
225
? ?? = 40
°
??
Q2: An ideal gas initially at ?? °
?? temperature, is compressed suddenly to one fourth of
its volume. If the ratio of specific heat at constant pressure to that at constant volume
is ?? /?? , the change in temperature due to the thermodynamic process is ____ K.
Ans: 273
Solution:
We're given an ideal gas initially at ?? ?? = 0
°
C = 273 K. The gas is suddenly compressed to one-
fourth of its initial volume, and we are told that
?? =
?? ?? ?? ?? =
3
2
.
For an adiabatic process (one in which there is no heat exchange), if the process were reversible,
the relation between the temperature and volume would be
?? ?? ?? -1
= constant.
Even though the compression is "sudden" (and hence irreversible), the final equilibrium state of
the gas is uniquely determined by its internal energy (which is a state function). That allows us
to use the adiabatic relation between the initial and final states.
Here are the steps:
Write the adiabatic relation between the initial and final states:
?? ?? ?? ?? ?? -1
= ?? ?? ?? ?? ?? -1
.
Since the gas is compressed to one-fourth of its volume, we have
?? ?? =
1
4
?? ?? .
Substitute this into the adiabatic relation:
273 ?? ?? ?? -1
= ?? ?? (
1
4
?? ?? )
?? -1
.
With ?? =
3
2
,
?? - 1 =
3
2
- 1 =
1
2
.
So the relation becomes:
273 ?? ?? 1/2
= ?? ?? (
1
4
)
1/2
?? ?? 1/2
.
Cancel the common factor ?? ?? 1/2
(provided it is nonzero) and simplify:
273 = ?? ?? (
1
2
).
Now solve for the final temperature ?? ?? :
?? ?? = 273× 2 = 546 K.
The change in temperature is then:
??? = ?? ?? - ?? ?? = 546 - 273 = 273 K.
So, the change in temperature due to the thermodynamic process is 273 K .
Q3: The temperature of 1 mole of an ideal monoatomic gas is increased by ????
°
?? at
constant pressure. The total heat added and change in internal energy are ?? ?? and ?? ?? ,
respectively. If
?? ?? ?? ?? =
?? ?? then the value of ?? is ____ .
JEE Main 2025 (Online) 24th January Morning Shift
Ans: 15
Solution:
?? = ?? ?? ?? ??? and ??? = ?? ?? ?? ???
For a monoatomic ideal gas, the molar specific heats are given by:
?? ?? =
3
2
?? and ?? ?? = ?? ?? + ?? =
5
2
??
Thus, the ratio of the heat added to the change in internal energy is:
?? ??? =
?? ?? ?? ?? =
5
2
?? 3
2
?? =
5
3
Given that:
?? 1
?? 2
=
?? 9
We equate the two ratios:
5
3
=
?? 9
Multiplying both sides by 9 :
?? =
5
3
× 9 = 15
Thus, the value of ?? is ???? .
Q4: A container of fixed volume contains a gas at ????
°
?? . To double the pressure of the
gas, the temperature of gas should be raised to ____
°
?? .
JEE Main 2025 (Online) 29th January Morning Shift
Ans: 327
Solution:
To solve this problem, we can use the combined gas law in terms of pressure ( ?? ) and
temperature ( ?? ). For a gas with a fixed volume, the relationship is given as:
?? 1
?? 1
=
?? 2
?? 2
where:
?? 1
is the initial pressure,
?? 1
is the initial temperature in Kelvin,
?? 2
is the final pressure,
?? 2
is the final temperature in Kelvin.
Given that the initial temperature ?? 1
= 27
°
?? , we need to convert it to Kelvin:
?? 1
= 27
°
?? + 273 .15 = 300 .15 K
The final pressure ?? 2
is twice the initial pressure ( ?? 2
= 2?? 1
). Substituting these values into the
gas law equation gives:
?? 1
300 .15
=
2?? 1
?? 2
Solving for ?? 2
:
Cancel ?? 1
from both sides:
1
300 .15
=
2
?? 2
Rearrange to solve for ?? 2
:
?? 2
= 2 × 300 .15 = 600.3 K
Convert the final temperature back to Celsius:
?? 2
= 600.3 K - 273 .15 = 327 .15
°
C
Therefore, to double the pressure of the gas, the temperature should be raised to
approximately ??????
°
?? .
Q5: ?? ?? is the specific heat ratio of monoatomic gas A having 3 translational degrees of
freedom. ?? ?? is the specific heat ratio of polyatomic gas ?? having 3 translational, 3
rotational degrees of freedom and ?? vibrational mode. If
?? ?? ?? ?? = (?? +
?? ?? ), then the value
of ?? is ____ .
JEE Main 2025 (Online) 2nd April Morning Shift
Ans: 3
Solution:
To determine the value of ?? , we start by considering the specific heat ratios for gases A and B .
For gas A , which is monoatomic with 3 translational degrees of freedom:
The degrees of freedom, ?? ?? , is 3 .
Therefore, ?? ?? =
?? ?? +2
?? ?? =
3+2
3
=
5
3
.
For gas B , which is polyatomic with 3 translational, 3 rotational degrees of freedom, and 1
vibrational mode:
The total degrees of freedom, ?? ?? , is 3 + 3 + 2 × 1 = 8 (since one vibrational mode contributes
2 degrees of freedom: 1 kinetic +1 potential).
Page 5
JEE Main Previous Year Questions
(2025): Thermodynamics
Q1:Three conductors of same length having thermal conductivity ?? ?? , ?? ?? and ?? ?? are
connected as shown in figure.
Area of cross sections of 1
st
and 2
nd
3
rd
conductor it is double of the 1
st
conductor. The
temperatures are given in the figure. In steady state condition, the value of ?? is ____
°
C. (Given :
k
1
= 60Js
-1
m
-1
K
-1
, k
2
= 120 Js
-1
m
-1
K
-1
, k
3
= 135 Js
-1
m
-1
K
-1
) conductor are same
and for
Ans: 40
?? 1
=
2?? ?? 1
??
(As ?? 1
= ?? 2
= ?? 3
= ??
?? 1
= ?? 2
= ?? /2
?? 3
= ?? )
?? 2
=
2?? ?? 2
??
?? 3
=
?? ?? 3
??
?? 1
+ ?? 2
= ?? 3
?
100- ?? 2?? ?? 1
?? +
100- ?? 2?? ?? 2
?? =
?? - 0
?? ?? 3
??
?
100- ?? 2
( ?? 1
+ ?? 2
) = ?? 3
??
? 50( ?? 1
+ ?? 2
)= ?? [?? 3
+
?? 1
+ ?? 2
2
]
? 50( 60 + 120 ) = ?? [135+
60 + 120
2
]
? 50 × 80 = ?? ( 135+ 90)
? ?? =
50 × 180
225
? ?? = 40
°
??
Q2: An ideal gas initially at ?? °
?? temperature, is compressed suddenly to one fourth of
its volume. If the ratio of specific heat at constant pressure to that at constant volume
is ?? /?? , the change in temperature due to the thermodynamic process is ____ K.
Ans: 273
Solution:
We're given an ideal gas initially at ?? ?? = 0
°
C = 273 K. The gas is suddenly compressed to one-
fourth of its initial volume, and we are told that
?? =
?? ?? ?? ?? =
3
2
.
For an adiabatic process (one in which there is no heat exchange), if the process were reversible,
the relation between the temperature and volume would be
?? ?? ?? -1
= constant.
Even though the compression is "sudden" (and hence irreversible), the final equilibrium state of
the gas is uniquely determined by its internal energy (which is a state function). That allows us
to use the adiabatic relation between the initial and final states.
Here are the steps:
Write the adiabatic relation between the initial and final states:
?? ?? ?? ?? ?? -1
= ?? ?? ?? ?? ?? -1
.
Since the gas is compressed to one-fourth of its volume, we have
?? ?? =
1
4
?? ?? .
Substitute this into the adiabatic relation:
273 ?? ?? ?? -1
= ?? ?? (
1
4
?? ?? )
?? -1
.
With ?? =
3
2
,
?? - 1 =
3
2
- 1 =
1
2
.
So the relation becomes:
273 ?? ?? 1/2
= ?? ?? (
1
4
)
1/2
?? ?? 1/2
.
Cancel the common factor ?? ?? 1/2
(provided it is nonzero) and simplify:
273 = ?? ?? (
1
2
).
Now solve for the final temperature ?? ?? :
?? ?? = 273× 2 = 546 K.
The change in temperature is then:
??? = ?? ?? - ?? ?? = 546 - 273 = 273 K.
So, the change in temperature due to the thermodynamic process is 273 K .
Q3: The temperature of 1 mole of an ideal monoatomic gas is increased by ????
°
?? at
constant pressure. The total heat added and change in internal energy are ?? ?? and ?? ?? ,
respectively. If
?? ?? ?? ?? =
?? ?? then the value of ?? is ____ .
JEE Main 2025 (Online) 24th January Morning Shift
Ans: 15
Solution:
?? = ?? ?? ?? ??? and ??? = ?? ?? ?? ???
For a monoatomic ideal gas, the molar specific heats are given by:
?? ?? =
3
2
?? and ?? ?? = ?? ?? + ?? =
5
2
??
Thus, the ratio of the heat added to the change in internal energy is:
?? ??? =
?? ?? ?? ?? =
5
2
?? 3
2
?? =
5
3
Given that:
?? 1
?? 2
=
?? 9
We equate the two ratios:
5
3
=
?? 9
Multiplying both sides by 9 :
?? =
5
3
× 9 = 15
Thus, the value of ?? is ???? .
Q4: A container of fixed volume contains a gas at ????
°
?? . To double the pressure of the
gas, the temperature of gas should be raised to ____
°
?? .
JEE Main 2025 (Online) 29th January Morning Shift
Ans: 327
Solution:
To solve this problem, we can use the combined gas law in terms of pressure ( ?? ) and
temperature ( ?? ). For a gas with a fixed volume, the relationship is given as:
?? 1
?? 1
=
?? 2
?? 2
where:
?? 1
is the initial pressure,
?? 1
is the initial temperature in Kelvin,
?? 2
is the final pressure,
?? 2
is the final temperature in Kelvin.
Given that the initial temperature ?? 1
= 27
°
?? , we need to convert it to Kelvin:
?? 1
= 27
°
?? + 273 .15 = 300 .15 K
The final pressure ?? 2
is twice the initial pressure ( ?? 2
= 2?? 1
). Substituting these values into the
gas law equation gives:
?? 1
300 .15
=
2?? 1
?? 2
Solving for ?? 2
:
Cancel ?? 1
from both sides:
1
300 .15
=
2
?? 2
Rearrange to solve for ?? 2
:
?? 2
= 2 × 300 .15 = 600.3 K
Convert the final temperature back to Celsius:
?? 2
= 600.3 K - 273 .15 = 327 .15
°
C
Therefore, to double the pressure of the gas, the temperature should be raised to
approximately ??????
°
?? .
Q5: ?? ?? is the specific heat ratio of monoatomic gas A having 3 translational degrees of
freedom. ?? ?? is the specific heat ratio of polyatomic gas ?? having 3 translational, 3
rotational degrees of freedom and ?? vibrational mode. If
?? ?? ?? ?? = (?? +
?? ?? ), then the value
of ?? is ____ .
JEE Main 2025 (Online) 2nd April Morning Shift
Ans: 3
Solution:
To determine the value of ?? , we start by considering the specific heat ratios for gases A and B .
For gas A , which is monoatomic with 3 translational degrees of freedom:
The degrees of freedom, ?? ?? , is 3 .
Therefore, ?? ?? =
?? ?? +2
?? ?? =
3+2
3
=
5
3
.
For gas B , which is polyatomic with 3 translational, 3 rotational degrees of freedom, and 1
vibrational mode:
The total degrees of freedom, ?? ?? , is 3 + 3 + 2 × 1 = 8 (since one vibrational mode contributes
2 degrees of freedom: 1 kinetic +1 potential).
Therefore, ?? ?? =
?? ?? +2
?? ?? =
8+2
8
=
10
8
=
5
4
.
Now, the relation given is:
?? ?? ?? ?? = (1 +
1
?? )
Substitute the values of ?? ?? and ?? ?? :
5
3
5
4
=
5
3
×
4
5
=
20
15
=
4
3
Equating to the given form:
4
3
= 1 +
1
??
Thus, we have:
4
3
- 1 =
1
??
1
3
=
1
??
Solving for ?? :
?? = 3
Hence, the value of ?? is 3 .
Q6: The internal energy of air in ?? ?? × ?? ?? × ?? ?? sized room at 1 atmospheric
pressure will be ____ × ????
?? ?? (Consider air as diatomic molecule)
JEE Main 2025 (Online) 2nd April Evening Shift
Ans: 12
Solution:
To determine the internal energy of the air in a room that measures 4 m× 4 m× 3 m at 1
atmospheric pressure, we can follow these steps using the properties of a diatomic gas:
The volume of the room, ?? , is calculated as:
?? = 4 m× 4 m× 3 m= 48 m
3
For a diatomic gas like air, the internal energy ?? is given by the formula:
?? = ?? ?? ?? ?? = ?? 5????
2
Where:
?? is the number of moles,
?? ?? is the molar heat capacity at constant volume,
?? is the ideal gas constant, and
?? is the temperature in Kelvin.
Using the ideal gas law, ???? = ?????? , we can substitute for ?????? :
?????? = ????
Therefore, the internal energy ?? becomes:
?? =
5
2
????
Substituting the given values for atmospheric pressure ?? = 10
5
Pa ( 1 atm ) and volume ?? =
Read More