Thermodynamics

19 JEE Main questions · Physics

Thermodynamic processes

PhysicsJEE Main 21 Jan 2026, Shift 2·Q25·Numerical·Easy–moderate
Open
A diatomic gas ( $\gamma = 1.4$ ) does 100 J of work when it is expanded isobarically. Then the heat given to the gas is J.
We corrected a printing error in the original paper
Source printed “the heat given to the gas ___ J” (“is” missing).
PhysicsJEE Main 22 Jan 2026, Shift 1·Q16·MCQ·Easy–moderate
Open
The volume of an ideal gas increases 8 times and temperature becomes $\left(\frac14\right)^{\text{th}}$ of initial temperature during a reversible change. If there is no exchange of heat in this process ( $\Delta Q = 0$ ) then identify the gas from the following options (Assuming the gases given in the options are ideal gases):
1. (1) $\ce{CO2}$
2. (2) $\ce{O2}$
3. (3) $\ce{NH3}$
4. (4)He
PhysicsJEE Main 23 Jan 2026, Shift 2·Q14·MCQ·Moderate
Open
One mole of an ideal diatomic gas expands from volume $V$ to $2V$ isothermally at a temperature $27^\circ$ C and does $W$ joule of work. If the gas undergoes same magnitude of expansion adiabatically from $27^\circ$ C doing the same amount of work $W$ , then its final temperature will be (close to) $^\circ$ C.
1. (1) $-189$
2. (2) $-56$
3. (3) $-30$
4. (4) $-117$
PhysicsJEE Main 24 Jan 2026, Shift 2·Q18·MCQ·Easy–moderate
Open
10 mole of an ideal gas is undergoing the process shown in the figure. The heat involved in the process from $P_1$ to $P_2$ is $\alpha$ Joule ( $P_1 = 21.7$ Pa and $P_2 = 30$ Pa, $C_v = 21$ J/K.mol, $R = 8.3$ J/mol.K). The value of $\alpha$ is .
1. (1)24
2. (2)15
3. (3)21
4. (4)28
PhysicsJEE Main 28 Jan 2026, Shift 1·Q12·MCQ·Moderate
Open
In the following $p$ - $V$ diagram the equation of state along the curved path is given by $(V-2)^2 = 4ap$ where $a$ is a constant. The total work done in the closed path is
1. (1) $-\dfrac{1}{a}$
2. (2) $+\dfrac{1}{3a}$
3. (3) $\dfrac{1}{2a}$
4. (4) $-\dfrac{1}{3a}$
PhysicsJEE Main 28 Jan 2026, Shift 2·Q22·Numerical·Easy–moderate
Open
A thermodynamic system is taken through the cyclic process ABC as shown in the figure. The total work done by the system during the cycle ABC is J.
PhysicsJEE Main 2 Apr 2026, Shift 1·Q22·Numerical·Moderate
Open
A vessel contains $0.15\ \mathrm{m^3}$ of a gas at pressure 8 bar and temperature $140^\circ$ C with $c_p = 3R$ and $c_v = 2R$ . It is expanded adiabatically till pressure falls to 1 bar. The work done during this process is kJ. ( $R$ is gas constant)
PhysicsJEE Main 6 Apr 2026, Shift 1·Q25·Numerical·Moderate
Open
A certain gas is isothermally compressed to $\left(\dfrac13\right)^{\text{rd}}$ of its initial volume ( $V_0 = 3$ litre) by applying required pressure. If the bulk modulus of the gas is $3\times10^{5}\ \mathrm{N/m^2}$ , the magnitude of work done on the gas is J.
PhysicsJEE Main 6 Apr 2026, Shift 2·Q5·MCQ·Easy–moderate
Open
A cylinder with adiabatic walls is closed at both ends and is divided into two compartments by a frictionless adiabatic piston. Ideal gas is filled in both (left and right) the compartments at same $P$ , $V$ , $T$ . Heating is started from left side until pressure changes to $\dfrac{27P}{8}$ . If initial volume of each compartment was 9 litres then the final volume in right-hand side compartment is litres. (for this ideal gas $C_P/C_V = 1.5$ )
1. (1)3
2. (2)4
3. (3)14
4. (4)9
PhysicsJEE Main 8 Apr 2026, Shift 2·Q11·MCQ·Moderate
Open
Initial pressure and volume of a monoatomic ideal gas are $P$ and $V$ . The change in internal energy of this gas in adiabatic expansion to volume $V_{\text{final}} = 27\,V$ is J.
1. (1) $-2PV\left(3\sqrt3 - 1\right)$
2. (2) $\dfrac43 PV$
3. (3) $-\dfrac43 PV$
4. (4) $\dfrac34 PV$

Laws of thermodynamics

PhysicsJEE Main 21 Jan 2026, Shift 1·Q24·Numerical·Easy–moderate
Open
10 mole of oxygen is heated at constant volume from $30^\circ$ C to $40^\circ$ C. The change in the internal energy of the gas is cal. (The molecular specific heat of oxygen at constant pressure, $C_p = 7$ cal./mol $^\circ$ C and $R = 2$ cal./mol $^\circ$ C.)
PhysicsJEE Main 23 Jan 2026, Shift 2·Q1·MCQ·Moderate
Open
The internal energy of a gas is 3nRT. One mole of this gas is kept in a cylinder having internal cross section area of $17\ \mathrm{cm^2}$ and fitted with a light movable frictionless piston. The gas is heated slowly by supplying 126 J heat. If the temperature rises by $4\ ^\circ$ C, then the piston will move cm.
(atmospheric pressure $= 10^{5}$ Pa)
1. (1)14.5
2. (2)1.55
3. (3)15.5
4. (4)1.45
We corrected a printing error in the original paper
Source printed “The internal energy of a monoatomic gas is 3nRT. One mole of helium is kept”; corrected to the intended “The internal energy of a gas is 3nRT. One mole of this gas is kept” (a monoatomic gas has $U = \tfrac32 nRT$ , which gives 44.8 cm, no option; the key 15.5 uses $U = 3nRT$ ); “suppling”.
PhysicsJEE Main 24 Jan 2026, Shift 1·Q4·MCQ·Moderate
Open
Density of water at $4^\circ$ C and $20^\circ$ C are $1000\ \mathrm{kg/m^3}$ and $998\ \mathrm{kg/m^3}$ respectively. The increase in internal energy of 4 kg water when it is heated from $4^\circ$ C to $20^\circ$ C is J.
(Specific heat capacity of water $= 4.2\ \mathrm{kJ\,kg^{-1}\,{}^\circ C^{-1}}$ and 1 atmospheric pressure $= 10^{5}$ Pa)
1. (1)315826.2
2. (2)234699.2
3. (3)258700.8
4. (4)268799.2
We corrected a printing error in the original paper
Source printed “1000 kg/m $^3$ and respectively” and “4.2 J/kg.”; corrected to the intended “1000 kg/m $^3$ and 998 kg/m $^3$ respectively” and “4.2 kJ kg $^{-1}$ $^\circ$ C $^{-1}$ ” (the values the key uses).
PhysicsJEE Main 24 Jan 2026, Shift 2·Q21·Numerical·Easy–moderate
Open
When 300 J of heat given to an ideal gas with $C_p = \dfrac72 R$ its temperature raises from $20\ ^\circ$ C to $50\ ^\circ$ C keeping its volume constant. The mass of the gas is (approximately) g. ( $R = 8.314$ J/mol.K).
Flawed question. Asks for the mass of the gas but no molar mass is given (only $n \approx 0.481$ mol follows); the printed key 481 matches no stated quantity, so there is no evident intended version. It is shown for completeness and is left out of practice tests.
PhysicsJEE Main 2 Apr 2026, Shift 1·Q8·MCQ·Easy–moderate
Open
Heat is supplied to a diatomic gas at constant pressure. Then the ratio of $\Delta Q : \Delta U : \Delta W$ is .
1. (1)2 : 3 : 5
2. (2)5 : 3 : 2
3. (3)2 : 5 : 7
4. (4)7 : 5 : 2
PhysicsJEE Main 2 Apr 2026, Shift 2·Q23·Numerical·Easy–moderate
Open
5 moles of unknown gas is heated at constant volume from $10^\circ$ C to $20^\circ$ C. The molar specific heat of this gas at constant pressure $c_p = 8$ cal/mol. $^\circ$ C and $R = 8.36$ J/mol. $^\circ$ C. The change in the internal energy of the gas is calorie.
PhysicsJEE Main 5 Apr 2026, Shift 1·Q7·MCQ·Easy–moderate
Open
Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : Change in internal energy of a system containing $n$ mole of ideal gas can be written as $\Delta U = nC_v(T_f - T_i) = \dfrac{nR}{\gamma - 1}(T_f - T_i)$ , where $\gamma = \dfrac{C_P}{C_v}$ , $T_i$ = initial temperature, $T_f$ = final temperature.
Reason R : Relation between degree of freedom $f$ and $\gamma\ (= C_p/C_v)$ is $\left(\gamma = 1 + \dfrac{2}{f}\right)$
Choose the correct answer from the options given below
1. (1)Both A and R are true and R is the correct explanation of A
2. (2)Both A and R are true but R is NOT the correct explanation of A
3. (3)A is true but R is false
4. (4)A is false but R is true
We corrected a printing error in the original paper
Source labelled the two statements “Statement I” and “Statement II” (the lead-in and options use Assertion A / Reason R); source printed “ttue” in option (4).
PhysicsJEE Main 5 Apr 2026, Shift 1·Q8·MCQ·Easy–moderate
Open
Consider the following statements:
- (A)Zeroth law of thermodynamics gives concept of temperature
- (B)First law of thermodynamics gives concept of internal energy
- (C)In isothermal expansion of ideal gas, $\Delta Q \neq \Delta W$
- (D)Product of intensive and extensive variables is extensive
- (E)The ratio of any extensive variable to mass will be an extensive variable
Choose the correct combination of statements from the options given below:
1. (1)C, D and E Only
2. (2)A, B and C Only
3. (3)A, B and D Only
4. (4)B, C and D Only
PhysicsJEE Main 8 Apr 2026, Shift 2·Q10·MCQ·Moderate
Open
One mole of diatomic gas having rotational modes only is kept is a cylinder with a piston system. The cross-section area of the cylinder is $4\ \mathrm{cm^2}$ . The gas is heated slowly to raise the temperature by $1.2\ ^\circ$ C during which the piston moves by 25 mm. The amount of heat supplied to the gas is J. (Atmospheric pressure $= 100$ kPa, $R = 8.3$ J/mol.K) (Neglect mass of the piston)
1. (1)24.8
2. (2)25
3. (3)15.04
4. (4)29.98
Flawed question. The data are inconsistent: with a free piston at 100 kPa, $P\Delta V$ must equal $nR\Delta T = 9.96$ J, but a 25 mm travel gives 1.0 J; no option equals the consistent $Q = 34.9$ J, and the key 25 is only the option nearest to $24.9 + 1.0 = 25.9$ J. It is shown for completeness and is left out of practice tests.