Physics is where JEE ranks are usually won or lost, since a single conceptual slip changes the whole answer. Questions here span mechanics, rotational motion, thermodynamics, waves and oscillations, electrostatics, current electricity, magnetism, optics, and modern physics. Numerical problems carry full derivations so you can see which step you skipped, not just which option was right.
A gas undergoes an isothermal process at 300 K. If the initial volume is 2 L and final volume is 5 L, what is the work done by the gas? (Take R = 8.314 J/(mol·K), n = 1 mol)
In an adiabatic process with a diatomic ideal gas (γ = 1.4), if the initial temperature is 300 K and volume increases by factor of 2, what is the final temperature?
A cyclic process consists of two isothermal and two adiabatic processes (Carnot cycle). What is true about the heat exchanges?
Answer: A
In Carnot cycle, isothermal processes involve heat exchange with reservoirs (Q₁ at hot reservoir, Q₂ at cold reservoir), while adiabatic processes have no heat exchange (Q=0)
Q.4Medium
In an isobaric process, 5 moles of a monoatomic ideal gas are heated from 300 K to 400 K. What is the heat supplied? (R = 8.314 J/(mol·K))
For a van der Waals gas, which statement is correct?
Answer: A
Van der Waals equation (P + a/V²)(V - b) = RT accounts for molecular volume (b term) and intermolecular attractive forces (a term)
Q.9Medium
In an expansion process, a gas does 500 J of work and absorbs 300 J of heat. What is the change in internal energy?
Answer: A
Using first law: ΔU = Q - W = 300 - 500 = -200 J (internal energy decreases)
Q.10Medium
During an isobaric expansion of an ideal gas, the work done by the gas is 400 J. If pressure is constant at 2 atm, what is the change in volume? (1 atm = 101325 Pa)
Answer: B
W = PΔV. Here W = 400 J, P = 2 × 101325 = 202650 Pa. So ΔV = W/P = 202650400 ≈ 0.00197 m³
Q.11Medium
For a diatomic ideal gas undergoing an isothermal process, which quantity remains constant?
Answer: C
In an isothermal process, temperature is constant. For an ideal gas, internal energy depends only on temperature, so ΔU = 0. Pressure and volume change according to PV = constant.
Q.12Medium
Two samples of the same ideal gas at the same temperature have volumes V and 2V respectively. The ratio of their internal energies is:
Answer: D
Internal energy U = nCvT. Without knowing the number of moles in each sample, the ratio cannot be determined. Same temperature doesn't mean same internal energy.
Q.13Medium
A heat engine absorbs 1000 J of heat and rejects 600 J to the cold reservoir in one cycle. What is its efficiency?
The entropy change for a reversible isothermal process is given by:
Answer: C
For reversible isothermal process: ΔS = Q/T = nR ln(Vf/Vi) since Q = nRT ln(Vf/Vi) for ideal gas isothermal expansion.
Q.15Medium
Which process would result in the maximum work output from an ideal gas expansion between two fixed pressures?
Answer: A
For expansion between fixed initial and final states, isothermal process yields maximum work because the gas maintains maximum pressure throughout the expansion compared to adiabatic or other processes.
Q.16Medium
A cylinder with a movable piston contains 2 moles of ideal gas at 300 K and 1 atm. When heated at constant pressure to 600 K, what is the work done by the gas? (R = 8.314 J/mol·K)
Two identical blocks of metal at different temperatures are brought into thermal contact in an isolated system. The process is:
Answer: C
Heat transfer between objects at different temperatures is irreversible. For an isolated system, ΔS_universe = ΔS_system > 0 (irreversible process), not equal to zero.
