Thermodynamics Multiple Choice Questions and Answers

PART A

Question 1
In a given process on an ideal gas, $dW>0$ and $dQ=0$.Then for the gas
a) Temperature will decrease
b) Temperature will increase
c) volume will decrease
d) none of above

Question 2
A cylinder of diameter $D$ and of thermal conductivity $k$ is surrounded by a cylindrical shell of inner diameter $D$ and Outer Diameter $2D$ made of material of thermal conductivity $2k$. The effective thermal conductivity of the system is
a) 5k/3
b) 4k
c) 5k/4
d) 7k/4

Question 3
What all is true for an adiabatic process
a) $dQ=0$
b) $dW=-nCvdT$
c) $TV^{y-1}=constant$
d) all the above three

Question 4
what is the ratio of r.m.s speed of $H_2$ to $O_2$
a) 4:1
b) 1:4
c) 2:1
d) 1:2

Question 5
The coefficient of linear expansion of an inhomogeneous rod changes linearly from ⓫ to &#9452 from one end to the other end of the rod.The effective coefficient of linear expansion of the rod is

a ⓫+⓬
b 1/2(⓫+⓬)
c. √⓫⓬
d. (⓫-⓬)

Answers
1.a
dU=dQ-dW
2.d
3.d
4.a hint $V_{rms}=\sqrt{\frac{3RT}{M}}$
5.b

PART B

1. An ideal gas is taken through the cycle ABCDA. calculate the work done by the gas

a. (3PV)
b. (2PV)
c. (PV)
d. none of the above

2. An ideal gas was taken from state A to state B in three ways. If W1, W2, W3 are work done by the gas in patch ABC, ADC, and AC respectively. Which one of the following is true

a. W1 > W2 > W3
b. W1 > W3 > W2
c. W3 > W2 > W1
d. None of the above

3. An ideal gas is taken through the cycle ABA. Calculate the work done by the gas

a 2pv-1/2&#960v2
b 2pv+1/2&#960v2
c 2pv
d None of the above

4. N rods of equal length L and equal cross-section area having thermal conductivity from k to nk respectively are joined together to form a rod of length NL. What is the ratio of Thermal conductivity of the whole rod to the thermal conductivity of Nth Rod?
   a.1/2(n+1)
   b.n+1
   c.n
   d.1

5.The speed of the four molecules is v, 2v, 3v, 4v. What is the rms speed of the gas
a.v√7
b. 7v
c.v√2
d.v√7.5

6.A sample of gas expands from volume V1 to V2. The amount of work done by the gas is greatest when the expansion is
a. Isothermal
b.Adiabatic
c. Isobaric
d. Equal in all the cases

7.A sample of an ideal gas has volume 2V, Pressure 2P and Temperature T.The mass of each molecule of the gas is m.The density of the gas is
a. mkT
b. 2P/kt
c. P/kVT
d. 2Pm/kT

8. EN and EH respectively are the average kinetic energy of the molecules of Nitrogen and Hydrogen.if the two gas are at the same temperature which of the following statement is true?
   a. EN > EH
   b. EN = EH
   c. EN < EH
   d. Nothing can be said
9. One mole of a diatomic gas is taken through the process PTn=C where n and C are constant.if the heat capacity of the gas is negative,then the value of n may be
   a. 4
   b. 3
   c. -4
   d. -3
10. Certain Ideal gas is found to be obey PV3/2=C during an adiabatic process.If such a gas at initial temperature T is adiabatically compressed to half the initial volume.Its final temperature will be
    a. T√2
    b. 2T
    c. 2T√2
    d. 4T

Answer

1. b
   Hint:Work done is area enclosed
2. b
   Hint: Work done is area enclosed
   3.d
   Hint: Work done is area enclosed
   4.a
   5.d
   6.c
   7.d
   8.b
   9.c
   hint for PVn=constant,Molar Specific Heat=R/y-1 + R/1-n
   10 a
   hint for TVy-1=constant