Practice <strong>NEET UG Physics</strong> MCQ questions covering Mechanics, Thermodynamics, Waves & Optics, Modern Physics, Electricity & Magnetism, and Electromagnetic Induction. Aligned with NCERT Class 11 & 12 Physics syllabus.
For a Carnot engine operating between temperatures T₁ (hot) and T₂ (cold), the maximum efficiency is:
Answer: A
Maximum (Carnot) efficiency: η_max = 1 - T_cold/T_hot = 1 - T₂/T₁. This is the theoretical maximum for any heat engine.
Q.44Medium
A system absorbs 1000 J of heat and does 600 J of work on the surroundings. What is the change in internal energy?
Answer: A
ΔU = Q - W = 1000 - 600 = 400 J. When work is done BY the system, it's subtracted from heat absorbed.
Q.45Medium
What is the relationship between Cp and Cv for an ideal gas?
Answer: D
Both relationships are true: Cp - Cv = R (molar basis) and Cp/Cv = γ. For monoatomic gas, γ = 35; for diatomic, γ = 57.
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Q.46Medium
In an adiabatic expansion of an ideal gas, the temperature decreases. This is because:
Answer: B
In adiabatic process, Q = 0. Since ΔU = -W and W > 0 (expansion), ΔU < 0, so temperature decreases. Internal energy decreases as work is done by the gas.
Q.47Hard
A refrigerator operates between 300 K and 250 K. What is the minimum work required to remove 1000 J of heat from the cold reservoir in one cycle?
Answer: A
For Carnot refrigerator: COP = T_cold/(T_hot - T_cold) = 50250 = 5. So W = Q_cold/COP = 51000 = 200 J.
Q.48Medium
Which process is NOT isobaric (constant pressure)?
Answer: C
Expansion in a rigid container is isochoric (constant volume), not isobaric. Phase changes and open systems typically occur at constant pressure.
Q.49Medium
The Joule-Thomson coefficient for an ideal gas is:
Answer: C
For ideal gases, μ_JT = 0 because they have no intermolecular forces. Real gases show non-zero values depending on temperature and pressure conditions.
Q.50Medium
A gas mixture contains N₂ and O₂. For the mixture, Cv would be:
Answer: A
For gas mixtures: Cv(mix) = Σ(n_i × Cv_i)/Σn_i. The heat capacity is the weighted sum based on composition.
Q.51Hard
In a polytropic process PVⁿ = constant. If n = γ, the process is:
Answer: C
For a polytropic process with n = γ = Cp/Cv, the process follows PVʸ = constant, which is the equation for an adiabatic process.
Q.52Medium
The entropy of an isolated system:
Answer: A
According to the second law of thermodynamics: ΔS_universe ≥ 0. For isolated systems, ΔS_system ≥ 0 (increases for irreversible, constant for reversible).
Q.53Hard
Which of the following processes would have the maximum work done by the gas for the same initial and final states?
Answer: A
For same initial and final states, isothermal process produces maximum work because the gas expands at the highest average pressure. W_isothermal > W_adiabatic for expansion.
Q.54Hard
The standard enthalpy change of reaction ΔH° = -200 kJ/mol. This reaction is:
Answer: C
Negative ΔH° indicates exothermic reaction. Spontaneity depends on both ΔH and ΔS (ΔG = ΔH - TΔS). Low T reactions with negative ΔH are more likely spontaneous.
Q.55Medium
For a system undergoing a cyclic process, which of the following must be true?
Answer: B
In a cyclic process, the system returns to initial state, so ΔU = 0 (state function). From first law: Q = W. Heat absorbed equals work done by the system.
Q.56Medium
A substance has ΔH_fusion = 6 kJ/mol and melts at 300 K. The entropy change for melting is approximately:
Answer: A
For phase change at equilibrium: ΔS = ΔH/T = 6000 J / 300 K = 20 J/(mol·K). This applies at the melting point where both phases are in equilibrium.
Q.57Easy
A system absorbs 500 J of heat and does 200 J of work on the surroundings. What is the change in internal energy of the system?
Answer: A
By first law of thermodynamics: ΔU = q - w = 500 - 200 = 300 J (where w is work done by the system)
Q.58Easy
Which of the following is a state function?
Answer: C
Internal energy depends only on initial and final states, not on the path. Heat and work are path functions.
Q.59Medium
For an adiabatic process of an ideal gas, which relationship is correct?
Answer: A
For an adiabatic process: PV^γ = constant leads to TV^(γ-1) = constant when combined with ideal gas law.
Q.60Medium
The molar heat capacity of a gas at constant pressure (Cp) is greater than at constant volume (Cv) because:
Answer: B
At constant pressure, supplied heat does two things: increases internal energy and does expansion work. Hence Cp > Cv by amount R.
