Thermodynamics — Set 1
Physics · ऊष्मागतिकी · Questions 1–10 of 40
Which equation correctly represents the first law of thermodynamics when W is the work done by the system?
Correct Answer: C. Q = ΔU + W
The first law states that heat added equals increase in internal energy plus work done by the system. This is written as Q = ΔU + W with this sign convention. It expresses conservation of energy in thermodynamic processes.
Internal energy of a thermodynamic system is best classified as which type of quantity?
Correct Answer: D. State function
Internal energy depends only on the state of the system, so it is a state function. It does not depend on the path followed between states. Heat and work are common examples of path functions.
For an ideal gas undergoing an isothermal process, what is the change in internal energy?
Correct Answer: D. It is zero
The correct answer is 'It is zero'. For an ideal gas, internal energy depends only on temperature, so it does not change in an isothermal process. The temperature remains constant during the process. In this case, heat absorbed equals work done by the gas.
In an adiabatic process, which statement is correct about heat exchange?
Correct Answer: C. Heat exchanged is zero
An adiabatic process has no heat transfer between system and surroundings. This means Q = 0 for the process. Temperature can still change due to work done.
For a quasi-static process, the work done by a gas is given by which expression?
Correct Answer: C. W = ∫ P dV
In a quasi-static process, work is the integral of pressure with respect to volume change. This is written as W = ∫ P dV. On a P-V graph, it corresponds to the area under the curve.
In a complete cyclic process, what is the net change in internal energy of the working substance?
Correct Answer: A. It is zero
In a cyclic process the system returns to its initial state, so internal energy returns to the same value. Therefore the net change in internal energy is zero. Net heat absorbed equals net work done in the cycle.
Which expression correctly defines enthalpy (H) of a system?
Correct Answer: C. H = U + PV
Enthalpy is defined as the sum of internal energy and the product of pressure and volume. This is written as H = U + PV. It is especially useful for processes at constant pressure.
For an ideal gas, which relation between molar heat capacities is correct?
Correct Answer: D. Cp - Cv = R
For an ideal gas, the difference between molar heat capacities at constant pressure and volume equals the gas constant. This is known as Mayer’s relation, Cp - Cv = R. It follows from the first law and ideal gas behavior.
The ratio of heat capacities γ for a gas is defined as which quantity?
Correct Answer: A. γ = Cp/Cv
The heat capacity ratio γ is defined as Cp divided by Cv. It is important in adiabatic relations for gases. For common gases, γ is typically greater than 1.
For a monoatomic ideal gas, what is the molar heat capacity at constant volume (Cv)?
Correct Answer: D. Cv = 3R/2
A monoatomic ideal gas has three translational degrees of freedom, giving Cv = 3R/2 per mole. This follows from the equipartition idea for ideal gases. Then Cp becomes Cv + R, so Cp = 5R/2.