### Core Logic
Let's evaluate each process condition based on the first law of thermodynamics:
* **(A) Isothermal:** Continuous constant temperature (Delta T = 0$\Delta T = 0$) implies that the internal energy change of an ideal gas is zero, so Delta U = 0 implies text(IV)$\Delta U = 0 \implies \text{(IV)}$ [cite: 730].
* **(B) Adiabatic:** No thermal energy transfer occurs between the system and surroundings, meaning Delta Q = 0 implies text(II)$\Delta Q = 0 \implies \text{(II)}$ [cite: 731].
* **(C) Isobaric:** Constant pressure process where both volume and temperature typically vary, so internal energy changes continuously, Delta U neq 0 implies text(III)$\Delta U \neq 0 \implies \text{(III)}$ [cite: 732].
* **(D) Isochoric:** Rigid boundary condition at constant volume (Delta V = 0$\Delta V = 0$) ensures work done Delta W = PDelta V = 0 implies text(I)$\Delta W = P\Delta V = 0 \implies \text{(I)}$ [cite: 733].
Putting these together yields: (A)-(IV), (B)-(II), (C)-(III), (D)-(I)[cite: 155, 729].
### Pattern Recognition
Matching 'Isochoric' with zero work done (Delta W=0$\Delta W=0$) or 'Adiabatic' with zero heat exchange (Delta Q=0$\Delta Q=0$) are fundamental definitions that let you rapidly break down multi-choice grids[cite: 731, 733].
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Thermodynamics
Keywords:#isothermal internal energy change#JEE Main 2025 Evening Q17#isochoric process work done zero#adiabatic system heat exchange
More Thermodynamics Previous-Year Questions — Page 4
Q6jee_main_2025_24_jan_eveningAdiabatic Processes
Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : In an insulated container, a gas is adiabatically shrunk to half of its initial volume. The temperature of the gas decreases.
Reason (R) : Free expansion of an ideal gas is an irreversible and an adiabatic process.
In the light of the above statement, choose the correct answer from the options given below :
A. Both (A)$(A)$ and (R)$(R)$ are true and (R)$(R)$ is the correct explanation of (A)$(A)$
B.(A)$(A)$ is true but (R)$(R)$ is false
C.(A)$(A)$ is false but (R)$(R)$ is true
D. Both (A)$(A)$ and (R)$(R)$ are true but (R)$(R)$ is NOT the correct explanation of (A)$(A)$
Solution
### Related Formula
T_1 V_1^gamma-1 = T_2 V_2^gamma-1$$T_1 V_1^{\gamma-1} = T_2 V_2^{\gamma-1}$$
### Core Logic
Assertion (A) review:
An insulated container means the process is adiabatic (Q=0$Q=0$). When the gas is shrunk (compressed) to half its volume (V_2 = V_1 / 2$V_2 = V_1 / 2$),
T_2 = T_1 left(fracV_1V_2
ight)^gamma-1 = T_1 (2)^gamma-1$$T_2 = T_1 \left(\frac{V_1}{V_2}
ight)^{\gamma-1} = T_1 (2)^{\gamma-1}$$
Since gamma > 1$\gamma > 1$, T_2 > T_1$T_2 > T_1$. Therefore, temperature increases during adiabatic compression, which makes Assertion (A) false.
Reason (R) review:
Free expansion occurs when a gas expands into a vacuum inside an insulated container. No work is done (W=0$W=0$) and no heat is exchanged (Q=0$Q=0$), hence it is adiabatic. It cannot spontaneously reverse, so it is irreversible. Thus, Reason (R) is true.
### Pattern Recognition
Adiabatic compression always raises temperature due to work being done on the gas, while free expansion keeps the temperature of an ideal gas constant (dI=0$dI=0$ as W=0, Q=0$W=0, Q=0$).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Thermodynamics
Q13jee_main_2025_24_jan_eveningCyclic Processes
The magnitude of heat exchanged by a system for the given cyclic process ABCA (as shown in figure The image shows a P-V cycle consisting of a horizontal line from C to A and a semicircular loop from A back to C via B.) is (in SI unit)
A.10pi$10\pi$
B.5pi$5\pi$
C. zero
D.40pi$40\pi$
Solution
### Related Formula
From the first law of thermodynamics for a complete cycle:
Delta U = 0 implies Q = W = textArea of the loop$$\Delta U = 0 \implies Q = W = \text{Area of the loop}$$
### Core Logic
The graph shows a semicircle in a Ptext-V$P\text{-}V$ indicator diagram. The image shows a P-V cycle consisting of a horizontal line from C to A and a semicircular loop from A back to C via B.
- Pressure dimension diameter: Delta P = 400 - 200 = 200\ mathrmkPa = 200 times 10^3\ mathrmPa$\Delta P = 400 - 200 = 200\ \mathrm{kPa} = 200 \times 10^{3}\ \mathrm{Pa}$
- Volume dimension diameter: Delta V = 400 - 200 = 200\ mathrmcc = 200 times 10^-6\ mathrmm^3$\Delta V = 400 - 200 = 200\ \mathrm{cc} = 200 \times 10^{-6}\ \mathrm{m^3}$
Radius along Pressure axis: R_P = 100 times 10^3\ mathrmPa$R_P = 100 \times 10^3\ \mathrm{Pa}$
Radius along Volume axis: R_V = 100 times 10^-6\ mathrmm^3$R_V = 100 \times 10^{-6}\ \mathrm{m^3}$
Area of the closed semicircular path:
W = frac12 pi R_P R_V$$W = \frac{1}{2} \pi R_P R_V$$W = frac12 times pi times (100 times 10^3) times (100 times 10^-6)$$W = \frac{1}{2} \times \pi \times (100 \times 10^3) \times (100 \times 10^{-6})$$W = frac10pi2 = 5pi\ mathrmJ$$W = \frac{10\pi}{2} = 5\pi\ \mathrm{J}$$
Since Q = W$Q = W$, the heat exchanged has a magnitude of 5pi\ mathrmJ$5\pi\ \mathrm{J}$.
### Pattern Recognition
For a cycle on an indicator chart with mismatched scales, use the elliptic area template pi a b$\pi a b$ (or frac12pi a b$\frac{1}{2}\pi a b$ for a half-ellipse/semicircle).
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Thermodynamics
An ideal gas goes from an initial state to final state. During the process, the pressure of gas increases linearly with temperature.
A. The work done by gas during the process is zero.
B. The heat added to gas is different from change in its internal energy.
C. The volume of the gas is increased.
D. The internal energy of the gas is increased.
E. The process is isochoric (constant volume process)
Choose the correct answer from the options given below :-
A. A, B, C, D Only
B. A, D, E Only
C. E Only
D. A, C Only
Solution
### Related Formula
From the Ideal Gas Law:
PV = nRT$PV = nRT$
According to the First Law of Thermodynamics:
Delta Q = Delta U + W$$\Delta Q = \Delta U + W$$
### Core Logic
The question states that pressure increases linearly with temperature, which means their ratio is constant :
P = kT implies fracPT = textconstant$$P = kT \implies \frac{P}{T} = \text{constant}$$
Since fracPT = fracnRV$\frac{P}{T} = \frac{nR}{V}$, the volume V$V$ must remain constant throughout the process. This identifies it as an isochoric process (Statement E is true).
### Step 1: Evaluate All Statements
* Statement A: True. In an isochoric process, dV = 0 implies W = int P dV = 0$dV = 0 \implies W = \int P dV = 0$.
* Statement B: False. Since work is zero, the First Law simplifies to Delta Q = Delta U$\Delta Q = \Delta U$, meaning heat added equals the change in internal energy.
* Statement C: False. Volume is constant, so it does not increase.
* Statement D: True. As pressure increases linearly with temperature, temperature increases, which causes the internal energy of the gas to increase.
### Step 2: Final Selection
Gathering the true statements (A, D, and E) points directly to Option (2).
### Pattern Recognition
A linear P-T$P-T$ line passing through the origin always indicates a constant volume graph. For constant volume graphs, work done is zero, which simplifies the first law calculation.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Thermodynamics
Q25jee_main_2025_24_jan_morningSpecific Heat Capacities of Gases
The temperature of 1 mole of an ideal monoatomic gas is increased by 50^circC$50^{\circ}C$ at constant pressure. The total heat added and change in internal energy are E_1$E_{1}$ and E_2$E_{2}$, respectively. If fracE_1E_2=fracx9$\frac{E_{1}}{E_{2}}=\frac{x}{9}$ then the value of x is
Numerical Answer.Answer: 15 to 15
Solution
### Related Formula
For an ideal gas thermodynamic process:
* Total heat added at constant pressure (isobaric process) is :
E_1 = n C_P Delta T$$E_{1} = n C_{P} \Delta T$$
* Total change in internal energy is given by :
E_2 = n C_V Delta T$$E_{2} = n C_{V} \Delta T$$
The ratio of specific heat capacities is defined as:
gamma = fracC_PC_V $$\gamma = \frac{C_{P}}{C_{V}} $$
### Core Logic
Taking the ratio of the two energy expressions[cite: 179, 823]:
fracE_1E_2 = fracn C_P Delta Tn C_V Delta T = fracC_PC_V = gamma$$\frac{E_{1}}{E_{2}} = \frac{n C_{P} \Delta T}{n C_{V} \Delta T} = \frac{C_{P}}{C_{V}} = \gamma$$
### Step 1: Evaluating for a Monoatomic Gas
For an ideal monoatomic gas, the degrees of freedom are f = 3$f = 3$. This gives an adiabatic index of :
gamma = 1 + frac2f = 1 + frac23 = frac53 $$\gamma = 1 + \frac{2}{f} = 1 + \frac{2}{3} = \frac{5}{3} $$
Equating this value to the given ratio expression [cite: 179, 826]:
frac53 = fracx9$$\frac{5}{3} = \frac{x}{9}$$x = frac5 times 93 = 15$$x = \frac{5 \times 9}{3} = 15$$
### Pattern Recognition
The ratio of heat added to the change in internal energy during an isobaric process is always equal to the adiabatic exponent gamma$\gamma$ of the gas.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Thermodynamics
Qjee_main_2025_29_jan_morningAdiabatic Process
The workdone in an adiabatic change in an ideal gas depends upon only :
A. change in its pressure
B. change in its specific heat
C. change in its volume
D. change in its temperature
Solution
### Related Formula
Delta W = -Delta U = -n C_v Delta T$$\Delta W = -\Delta U = -n C_v \Delta T$$
### Core Logic
In an adiabatic system, no heat exchange occurs (Q=0$Q=0$). By the first law of thermodynamics, Delta W = -Delta U$\Delta W = -\Delta U$. Since internal energy U$U$ depends explicitly on temperature metrics, the total work output shifts uniquely based on temperature variation Delta T$\Delta T$.
### Chapter Mix
Class 11 Physics: Thermodynamics
More Thermodynamics Questions — jee_main_2025_07_april_evening
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