physics : class11 Monatomic Gas : Internal Energy : Thermodynamics MCQ Questions and Answers
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Monatomic Gas
MCQ questions and answers.
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MCQ Questions
1. What is the internal energy of n moles of an ideal monatomic gas at temperature T?
A.
nRT
B.
(3/2)nRT
C.
(5/2)nRT
D.
2nRT
Correct Answer:
(3/2)nRT
Explanation:
A monatomic ideal gas has three translational degrees of freedom, so its internal energy is U = (3/2)nRT.
2. The internal energy of an ideal monatomic gas depends only on its:
A.
Pressure
B.
Volume
C.
Temperature
D.
Pressure and volume independently
Correct Answer:
Temperature
Explanation:
For an ideal monatomic gas, internal energy is determined by the average translational kinetic energy of its atoms, which depends only on temperature.
3. How many degrees of translational freedom does each atom of a monatomic gas possess?
A.
One
B.
Two
C.
Three
D.
Six
Correct Answer:
Three
Explanation:
An atom in a monatomic gas can translate independently along the x, y, and z directions, giving three translational degrees of freedom.
4. What is the increase in internal energy when the temperature of n moles of an ideal monatomic gas increases by ΔT?
A.
nRΔT
B.
(3/2)nRΔT
C.
(5/2)nRΔT
D.
2nRΔT
Correct Answer:
(3/2)nRΔT
Explanation:
Since U = (3/2)nRT for a monatomic ideal gas, the change in internal energy is ΔU = (3/2)nRΔT.
5. What is the average translational kinetic energy of one atom of a monatomic ideal gas at temperature T?
A.
kT
B.
(1/2)kT
C.
(3/2)kT
D.
3kT
Correct Answer:
(3/2)kT
Explanation:
Each of the three translational degrees of freedom contributes (1/2)kT, so the average energy per atom is (3/2)kT.
6. For an ideal monatomic gas, the molar heat capacity at constant volume is:
A.
R
B.
(3/2)R
C.
(5/2)R
D.
3R
Correct Answer:
(3/2)R
Explanation:
For a monatomic ideal gas, ΔU = nCᵥΔT and ΔU = (3/2)nRΔT, so Cᵥ = (3/2)R.
7. If the temperature of a fixed amount of an ideal monatomic gas is doubled, its internal energy becomes:
A.
Half its original value
B.
Unchanged
C.
Twice its original value
D.
Four times its original value
Correct Answer:
Twice its original value
Explanation:
The internal energy of a monatomic ideal gas is directly proportional to its absolute temperature, so doubling the temperature doubles the internal energy.
8. What is the internal energy of one mole of an ideal monatomic gas at temperature T?
A.
(1/2)RT
B.
RT
C.
(3/2)RT
D.
(5/2)RT
Correct Answer:
(3/2)RT
Explanation:
Using U = (3/2)nRT and setting n = 1 mole gives U = (3/2)RT.
9. An ideal monatomic gas is heated while its volume changes. The change in its internal energy is determined by the change in:
A.
Pressure only
B.
Volume only
C.
Temperature only
D.
Pressure and volume separately
Correct Answer:
Temperature only
Explanation:
Internal energy is a state function, and for an ideal monatomic gas it depends only on temperature, regardless of the path or volume change.
10. If the temperature of an ideal monatomic gas remains constant, its change in internal energy is:
A.
Positive
B.
Negative
C.
Zero
D.
Equal to its pressure
Correct Answer:
Zero
Explanation:
For an ideal monatomic gas, ΔU = (3/2)nRΔT. When temperature remains constant, ΔT = 0, so ΔU = 0.
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