Engineering Physics Questions and Answers – Ideal Gases – 2

This set of Engineering Physics Quiz focuses on “Ideal Gases – 2”.

1. In the upper part of the atmosphere, the kinetic temperature of the air is of the order 1000K. Therefore one feels extremely hot.
a) True
b) False
View Answer

Answer: b
Explanation: As we go up the atmosphere, the number of air molecules per unit volume decreases. The quantity oh heat per unit volume or the heat density is low. But the translational kinetic energy per molecule is quite large. As the kinetic temperature is the measure of translational kinetic energy, so the kinetic temperature is quite high in the upper atmosphere but one feels severe cold there due to low density.

2. What type of motion is associated with the molecules of gas?
a) Newton’s law of motion
b) Conservative motion
c) Linear motion
d) Brownian motion
View Answer

Answer: d
Explanation: Brownian motion is associated with the molecules of a gas. In this motion, any particular molecule will follow a zigzag path due to the collisions with the other molecules or with the walls of the container.

3. At room temperature, the rms speed of the molecules of a certain diatomic gas is found to be 1920ms-1. Which is the gas?
a) H2
b) F2
c) O2
d) Cl2
View Answer

Answer: a
Explanation: vrms=√(3RT/M)
M=3RT/(vrms)2 = (3×8.3×300)/(1920)2 = 2
Hence the gas is H2.
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4. A vessel contains a mixture of 1 mole of oxygen and 2 moles of nitrogen at 300 K. The ratio of the average rotational kinetic energy per O2 molecule to that per N2 molecule is?
a) 1:1
b) 1: 2
c) 2:1
d) Depends on the moment of inertia of the two molecules
View Answer

Answer: d
Explanation: Both gases are diatomic. Both have two rotational degrees of freedom at 300K. Average rotational kinetic energy per molecule of each gas will be same=2×1/2 kT=1kT
Hence the required ratio is 1:1.

5. Statement: For an ideal gas at constant temperature, the product of the pressure and volume is a constant.
Reason: The mean square velocity of the molecules is inversely proportional to mass.
a) Both statement and reason are true and explanation is the correct explanation of the statement
b) Both statement and reason are true but the explanation is not a correct explanation of the statement
c) Statement it true but the reason is false
d) Both statement and reason are false
View Answer

Answer: b
Explanation: Both the statement and reason are true but the explanation is not a correct explanation of the statement. According to Boyle’s law, PV=constant, at a given temperature.
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6. An ant is walking on the horizontal surface. The number of degrees of freedom of ant will be ___________
a) 1
b) 2
c) 3
d) 6
View Answer

Answer: b
Explanation: As the ant can move on a plane, it has 2 degrees of freedom.

7. The number of degrees of freedom for a diatomic gas molecule is ___________
a) 2
b) 3
c) 5
d) 6
View Answer

Answer: c
Explanation: A diatomic molecule has 3 degrees of freedom due to translator motion and 2 degrees of motion due to rotator motion.
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8. A gas at one atmosphere and having volume 100ml is mixed with another gas of equal moles at 0.5atm and having volume 50ml in flask of one litre, what is the final pressure?
a) 0.5atm
b) 1atm
c) 0.75atm
d) 0.125atm
View Answer

Answer: d
Explanation: Total number of moles is conserved.
(P1 V1)/RT+(P2 V2)/RT=PV/RT
(1×100)/RT+(0.5×50)/RT=(P×1000)/RT
P=0.125atm.

9. Temperature of oxygen kept in a vessel is raised by 1°C at constant volume. Heat supplied to the gas may be taken partly as translational and partly rotational kinetic energies. Their respective shares are ___________
a) 60%, 40%
b) 50%, 50%
c) 100%, zero
d) 40%, 60%
View Answer

Answer: a
Explanation: A diatomic oxygen molecule has 3 degrees of freedom due to translator motion and 2 degrees of freedom due to rotator motion. Their associated kinetic energies will be in the ratio 3:2 or 60% and 40%.
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10. An ideal gas is heated from 27°C to 627°C at constant pressure. If initial volume was 4m3, then the final volume of the gas will be?
a) 2m3
b) 4m3
c) 6m3
d) 12m3
View Answer

Answer: d
Explanation: Using Charle’s law,
V1/T1 = V2/T2
V2=T2/T1 ×V1=((273+627))/((273+27))×4=900/300×4=12m3.

Sanfoundry Global Education & Learning Series – Engineering Physics.

To practice all areas of Engineering Physics for Quizzes, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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