Thermodynamics Test

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Thermodynamics Test - 3

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Weekly Quiz Competition

Question 1
4 / -1

Refrigerators X and Y are removing 1000 J of heat from the freezer. Refrigerator X is working between -5° C and 25° C and refrigerator Y is working between -20° C and 20 °C. Find efficiency of refrigerator X and Y?

A
20,2

B
7.9,6.5

C
9.8,7.3

D
8.9,7.3

Solution

We know that the efficiency of refrigeration for a refrigerator is T₂ / T₁ + T₂
Where T₁ is source temperature and T₂ is sink temperature
For refrigerator X we have T₁ = 298K and T₂ = 268K
Hence the efficiency of refrigeration = 268 / 298 - 268
= 268 / 30
= 8.93
For refrigerator Y we have T₁ = 293K and T₂ = 253K
Hence the efficiency of refrigeration = 253 / 293 - 253
= 253 / 40
= 6.35
Question 2
4 / -1

Kelvin- Planck statement states that

A
The process whose sole result is transfer of heat from a colder object to a hotter object is not possible

B
Irreversible processes can be made reversible under certain conditions

C
No process is possible whose sole result is absorption of heat from a reservoir and all the heat is converted to work

D
Heat flows from colder body to hotter body

Solution

It works on the principle that no machine is 100% efficient. For instance if taking an ideal machine into consideration, work can be completely converted to heat. Now if the conditions are reversed, all heat cannot be converted to equal amount of work until and unless backed up by an external force.
Question 3
4 / -1

Which of the following is an example of heat pump?

A
Internal combustion engine

B
Blower heater

C
Refrigerator

D
Carnot engine

Solution

A heat pump is an electrical device that heats a building by pumping heat in from the cold outside. In other words, it’s the same as a refrigerator, but its purpose is to warm the hot reservoir rather than to cool the cold reservoir (even though it does both).
Question 4
4 / -1

For proper utilization of exergy, it is desirable to make first law efficiency ____ and the source and use temperatures should ____.

A
as close to unity, be different

B
as close to unity, match

C
as close to zero, match

D
as close to zero, be different

Solution

If first law efficiency is close to unity, the all the energy carried in by heat transfer is used and no heat is lost to the surroundings.
Question 5
4 / -1

The second law of thermodynamics says

A
Coefficient of performance can never be infinite for refrigerator

B
Heat released to the cold reservoir can be zero

C
Ideal gas can expand infinitely

D
Efficiency of a heat engine can be 100%.

Solution

The second law of thermodynamics gives a fundamental limitation to the efficiency of a heat engine and the coefficient of performance of a refrigerator. It says that the efficiency of a heat engine can never be unity or 100%, this implies that the heat released to the cold reservoir can never be made zero.
For a refrigerator the second law says that the coefficient through performance can never be infinite, this implies that the external work can never be zero.
Question 6
4 / -1

If the door of refrigerator is left open inside a closed room, what would happen to the temperature of the room?

A
Room temperature would decrease

B
Room temperature would increase

C
Room temperature would be same as the temperature inside the refrigerator

D
Room temperature would not be effected

Solution

If you leave the door open, heat is merely recycled from the room into the refrigerator, then back into the room. A net room temperature increase would result from the heat of the motor that would be constantly running to move energy around in a circle.
Question 7
4 / -1

Refrigerator transfers heat from the cold cooling coils to warm surroundings, which law of thermodynamics favour this process

A
Zeroth law of thermodynamics

B
Third law of thermodynamics

C
First law of thermodynamics

D
Second law of thermodynamics

Solution

Refrigerator follows the principle of Clausius statement of second law of thermodynamics. It does not violate second law of thermodynamics because it takes energy to transfer heat from low temperature body to high temperature body. Electrical work is given to refrigerator to extract heat from low temperature body and to transfer it to higher temperature body. If any refrigerator is transferring heat from low temperature body to higher temperature body without any external energy then we can say that it violates second law of thermodynamics. But in actual it takes energy to do.
Question 8
4 / -1

Which word is defined by this statement: A measure of this disorder, or randomness?

A
energy

B
enthalpy

C
mass

D
entropy

Solution

Entropy is defined as a thermodynamic property which serves as a measure of how close a system is to equilibrium, as well as a measure of the disorder in the system.
Question 9
4 / -1

What amount of work is needed to freeze 1 gm of water at 0˚C in a refrigerator .The temperature of surroundings is 320 K?

A
14.5 cal

B
13.77 cal

C
12.75 cal

D
10 cal
Question 10
4 / -1

The coefficient of performance of a refrigerator is given by

A

B
Q₂

C

D

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Thermodynamics Test - 3

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Question 1

20,2

7.9,6.5

9.8,7.3

8.9,7.3

Solution

Question 2

The process whose sole result is transfer of heat from a colder object to a hotter object is not possible

Irreversible processes can be made reversible under certain conditions

No process is possible whose sole result is absorption of heat from a reservoir and all the heat is converted to work

Heat flows from colder body to hotter body

Solution

Question 3

Internal combustion engine

Blower heater

Refrigerator

Carnot engine

Solution

Question 4

as close to unity, be different

as close to unity, match

as close to zero, match

as close to zero, be different

Solution

Question 5

Coefficient of performance can never be infinite for refrigerator

Heat released to the cold reservoir can be zero

Ideal gas can expand infinitely​

Efficiency of a heat engine can be 100%.

Solution

Question 6

Room temperature would decrease

Room temperature would increase

Room temperature would be same as the temperature inside the refrigerator

Room temperature would not be effected

Solution

Question 7

Zeroth law of thermodynamics

Third law of thermodynamics

First law of thermodynamics

Second law of thermodynamics

Solution

Question 8

energy

enthalpy

mass

entropy

Solution

Question 9

14.5 cal

13.77 cal

12.75 cal

10 cal

Question 10

Q2

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Ideal gas can expand infinitely

Q₂