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.
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.142Hard
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.143Medium
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.144Hard
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.145Hard
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.
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Q.146Medium
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.147Medium
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.148Easy
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.149Easy
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.150Medium
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.151Medium
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.
Q.152Easy
A carnot engine operates between two reservoirs at temperatures 400 K and 300 K. What is its maximum efficiency?
Which statement about entropy is correct for an isolated system?
Answer: B
Second law of thermodynamics: For an isolated system, ΔS ≥ 0 (entropy increases for irreversible processes, constant for reversible).
Q.154Medium
In an isothermal process of an ideal gas, the work done by the gas is:
Answer: B
For isothermal process: W = nRT ln(V_f/V_i) = nRT ln(P_i/P_f). Since ΔU = 0, q = W.
Q.155Medium
A gas undergoes compression where both pressure and temperature increase. This process is most likely:
Answer: D
In adiabatic compression (q=0), work is done on gas, increasing both P and T without heat exchange. Other processes would have different P-T relationships.
Q.156Medium
The coefficient of performance (COP) of a refrigerator is 5. If 100 J of work is done on it, how much heat is removed from the cold reservoir?
