Physics - Thermodynamics Question Paper 3

Exam Duration: 45 Mins Total Questions : 30

1 )

The internal energy change in a system that has absorbed 2 kcals of heat and done 500 J of work is :

(a)
6400 J
(b)
5400 J
(c)
7900 J
(d)
8900 J

2 )

A monoatomic gas of n-moles is heated from temperature T₁ to T₂ under two different conditions (i) at constant volume and (ii) at constant pressure. The change in internal energy of the gas is :

(a)
More for (i)
(b)
More for (ii)
(c)
Same in both cases
(d)
Independent of number of moles

3 )

Assertion: The efficiency of a heat engine can never be unity.
Reason: Efficiency of heat engine is fundamental limitation given by first law of thermodynamics.

(a)
If both assertion and reason are true and reason is the correct explanation of assertion.
(b)
If both assertion and reason are true but reason is not the correct explanation of assertion.
(c)
If assertion is true but reason is false.
(d)
If both assertion and reason are false

4 )

If a gas is compressed adiabatically by doing work of 150 J, the change in internal energy of the gas is

(a)
100 J
(b)
150 J
(c)
200 J
(d)
250 J

5 )

The specific heat of air at constant volume is 0.172 Cal g^-1 ^oC^-1. The change in internal energy when 5 g of air is heated from O°C to 4°C at constant volume is

(a)
28.8 J
(b)
14.4 J
(c)
7.2 J
(d)
3.51 J

6 )

An ideal gas system undergoes an isothermal process, then the work done during the process is

(a)
nRT In=\(\frac { { V }_{ 2 } }{ { V }_{ 1 } } \)
(b)
nRT In=\(\frac { { V }_{ 1 } }{ { V }_{2 } } \)
(c)
2nRT In=\(\frac { { V }_{ 2 } }{ { V }_{ 1 } } \)
(d)
2nRT In=\((\frac { { V }_{ 1 } }{ { V }_{2 } } )\)

7 )

If a carnot engine is working between steam point and ice point, then its efficiency will be:

(a)
24.9%
(b)
25.7%
(c)
26.8%
(d)
28.8%

8 )

A Carnot engine takes 900 kcal of heat from a reservoir at 723°C and exhausts it to a sink at 30^oC, The work done by the engine is

(a)
2.73 x 10⁶ Cal
(b)
3.73 x 10⁶ Cal
(c)
6.27 x 10⁵ Cal
(d)
3.73 x 10⁵Cal

9 )

In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas. If initial internal energy of the gas was 30 J, what will be the final internal energy?

(a)
42 J
(b)
12 J
(c)
10 J
(d)
18 J

10 )

An ideal gas A and a real gas B have their volumes increased from V to 2V under isothermal conditions. The increase in internal energy:

(a)
of A will be more than that of B
(b)
of B will be more than that of A
(c)
will be same in both A and B
(d)
will be zero in both the cases

11 )

A Carnot engine works first between 200°C and 0°C and then between 0°C and -200°C. The ratio of its efficiency in these two cases is:

(a)
1.0
(b)
0.721
(c)
0.577
(d)
0.34

12 )

If the degrees of freedom of a gas molecule be f then the ratio of two specific heats C_p / C_v is given by:

(a)
\(\frac{2}{f}\)+1
(b)
1-\(\frac{2}{f}\)
(c)
1+\(\frac{1}{f}\)
(d)
1-\(\frac{1}{f}\)

13 )

Isobaric modulus of elasticity is equal to:

(a)
isochoric modulus of elasticity
(b)
isothermal modulus of elasticity
(c)
zero
(d)
infinite

14 )

In the adiabatic compression, the decrease in volume is associated with:

(a)
increase in temperature and decrease in pressure
(b)
decrease in temperature and increase in pressure
(c)
decrease in temperature and decrease in pressure
(d)
increase in temperature and increase in pressure

15 )

In a cyclic process, work done by the system is:

(a)
zero
(b)
equal to heat given to the system
(c)
more than the heat given to the system
(d)
independent of heat given to the system

16 )

Which of the following process is correct for the given P - V diagram.

(a)
Adiabatic process
(b)
Isothermal process
(c)
Isobaric process
(d)
Isochoric process

17 )

Check the correct statement.

(a)
Internal energy is a path function, while heat is not
(b)
Heat is path function, while internal energy is not
(c)
Both heat and internal energy are path functions
(d)
Both heat and internal energy are not path functions

18 )

In Carnot engine efficiency is 40% at hot reservoir temperature T. For efficiency to be 50%, what will be the temperature of hot reservoir?

(a)
\(\frac{T}{5}\)
(b)
\(\frac{2T}{5}\)
(c)
6T
(d)
\(\frac{6T}{5}\)

19 )

In which of the following thermodynamic process of the gas, the work done is maximum?

(a)
Isothermal
(b)
Isobaric
(c)
Adiabatic
(d)
Isochoric

20 )

During the melting of a slab of ice at 273 K at atmospheric pressure:

(a)
positive work is done by the ice-water system on the atmosphere
(b)
positive work is done on the ice-water system by the atmosphere
(c)
internal energy of ice-water system decreases
(d)
none of the above

21 )

The change in the entropy of I mole of an ideal gas which went through an isothermal process from an initial state (P₁, V₁, T) to the final state (P₂, V₂, T) is equal to:

(a)
zero
(b)
R ln T
(c)
R ln \(\frac { { V }_{ 1 } }{ { V }_{ 2 } } \)
(d)
R ln \(\frac { { V }_{ 2 } }{ { V }_{ 1 } } \)

22 )

If C_p and C_v denote the specific heat of nitrogen per unit mass at constant pressure and constant volume respectively, then:

(a)
C_p-C_v=28R
(b)
C_p-C_v=R/28
(c)
C_p-C_v=R/14
(d)
C_p-C_v=R

23 )

Which of the following is not a state function?

(a)
Work done at constant pressure
(b)
Enthalpy
(c)
Work done by conservative force
(d)
Work done by non-conservative force

24 )

What is the most likely value for C_r (molar heat capacity at constant temperature)?

(a)
0
(b)
0 < C_r < C_v
(c)
C_v < C_r < C_p
(d)
infinity

25 )

The thermodynamic process in which no work is done on or by the gas is:

(a)
isothermal process
(b)
adiabatic process
(c)
cyclic process
(d)
isobaric process
(e)
isochoric process

26 )

A person of mass 70 kg wants to loss 5 kg by going up and down a 10m high stairs. He bums twice as much fat while going up than coming down. If 1 kg is burnt on expanding 7000 kilocalories, the number of times he must go up and down to reduce his weight by 4 kg is :