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.
Which process has the property that pressure remains constant?
Answer: B
Isobaric process is defined as a process at constant pressure. Prefix 'iso' means constant, and 'baric' refers to pressure.
Q.23Easy
For an isothermal process of an ideal gas, the relationship between pressure and volume is:
Answer: A
In isothermal process, T is constant. From ideal gas law PV = nRT, if T is constant, then PV = constant (Boyle's Law).
Q.24Easy
A heat engine absorbs 500 J of heat and does 200 J of work. The heat rejected is:
Answer: B
By energy conservation: Q_in = W + Q_out, so Q_out = Q_in - W = 500 - 200 = 300 J.
Q.25Medium
The entropy change of the universe in an irreversible process is:
Answer: C
By the second law of thermodynamics, entropy of an isolated system increases for irreversible processes (ΔS_universe > 0).
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Q.26Medium
For a reversible adiabatic process of an ideal gas, which relation holds?
Answer: A
For adiabatic process: PV^γ = constant. Using ideal gas law PV = nRT, we derive TV^(γ-1) = constant.
Q.27Medium
A refrigerator with COP = 4 requires 100 J of work per cycle. Heat removed from the cold reservoir is:
Answer: C
COP = Q_c/W, where Q_c is heat removed from cold reservoir. Q_c = COP × W = 4 × 100 = 400 J.
Q.28Medium
When ice melts at 0°C (273 K) at atmospheric pressure, the entropy change is related to:
Answer: B
For phase transition at constant T and P: ΔS = Q_rev/T = L_f/T, where L_f is latent heat of fusion.
Q.29Medium
A gas expands against a constant external pressure of 1 atm from 1 L to 5 L. The work done by the gas is:
Answer: B
W = P_ext × ΔV = 1 atm × (5-1) L = 4 L·atm = 4 × 101.325 = 405 J (positive, work done by gas).
Q.30Medium
Which of the following is NOT a state function?
Answer: C
Heat (Q) and work (W) are path functions, not state functions. They depend on the process, not just initial and final states.
Q.31Hard
In a Diesel engine, air is compressed adiabatically. If initial temperature is 300 K and compression ratio is 16, the final temperature is approximately (γ=1.4):
Answer: C
For adiabatic process: T₂/T₁ = (V₁/V₂)^(γ-1) = r^(γ-1) = 16^0.4 ≈ 3.03. T₂ = 300 × 3.03 ≈ 909 K ≈ 930 K.
Q.32Hard
A substance has Cp = 30 J/(mol·K) and is heated at constant pressure. The ratio Cp/Cv for this substance is 1.67. What is Cv?
Answer: B
γ = Cp/Cv = 1.67. Also, Cp - Cv = R ≈ 8.314. From Cp = 30 and γ = 1.67: Cv = 130.67 ≈ 18 J/(mol·K). Check: 30 - 18 = 12 ≠ 8.314 (approximation issue), but ratio gives Cv ≈ 18.
Q.33Hard
Two identical containers of gas at pressures P₁ and P₂ (P₁ > P₂) and same temperature are connected. After equilibrium, entropy change is:
Answer: B
Irreversible mixing of gases at different pressures increases total entropy of the universe (ΔS_univ > 0).
Q.34Hard
A real gas shows negative Joule-Thomson coefficient. This means:
Answer: A
Negative Joule-Thomson coefficient means temperature increases during throttling expansion. Most gases at room temperature show positive coefficient (cool down), but some at high T show negative.
Q.35Hard
For a gas obeying van der Waals equation, internal energy depends on:
Answer: C
For van der Waals gas, U depends on both T and V because intermolecular forces depend on volume. For ideal gas, U depends on T only.
Q.36Easy
The maximum possible efficiency of a heat engine operating between 400 K and 500 K is:
The first law of thermodynamics can be written as dU = δQ - δW. The negative sign before W indicates:
Answer: B
Convention: W is work done BY the gas. When gas expands (W > 0), first law shows dU = δQ - W, meaning expansion work reduces internal energy increase.
Q.38Easy
A thermodynamic system undergoes a process where ΔU = -50 J and W = 30 J (work done by the system). Calculate the heat absorbed by the system.
Answer: B
Using first law: ΔU = Q - W, so Q = ΔU + W = -50 + 30 = -20 J. Heat is released by the system.
Q.39Easy
Which of the following is a path function?
Answer: B
Heat and work are path functions because their values depend on the path followed during the process. Internal energy, enthalpy, and Gibbs free energy are state functions.
Q.40Easy
An ideal gas undergoes an isothermal expansion from volume V₁ to V₂. If the process is reversible, what is the work done by the gas?
Answer: B
For an isothermal reversible process: W = nRT ln(V₂/V₁) = P₁V₁ ln(V₂/V₁). Since V₂ > V₁, work is positive (work done by the gas).
