Thermodynamics Test

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Thermodynamics Test - 22

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Question 1
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Which of the following is an intensive property?

A
temperature

B
pressure

C
density

D
all of the above

Solution

$$Answer:-$$ D
An extensive property is a property that changes when the size of the sample changes. Examples are mass, volume, length, and total charge.
An intensive property doesn't change when you take away some of the sample. Examples are temperature, color, hardness, melting point, boiling point, pressure, molecular weight, and density. Because intensive properties are sometimes characteristic of a particular material, they can be helpful as clues in identifying unknown substances.
Question 2
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Which of the following is an intensive property?

A
mass

B
volume

C
length

D
pressure

Solution

$$Answer:-$$ D
An extensive property is a property that changes when the size of the sample changes. Examples are mass, volume, length, and total charge.
An intensive property doesn't change when you take away some of the sample. Examples are temperature, color, hardness, melting point, boiling point, pressure, molecular weight, and density. Because intensive properties are sometimes characteristic of a particular material, they can be helpful as clues in identifying unknown substances.
Question 3
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A 60J of heat is added to the system, resulting in 15J of work being done by the system. The remaining 45J of heat is released. Find out the efficiency of the system?

A
100%

B
75 %

C
45%

D
25%

E
15%

Solution

Amount of heat absorbed $$Q_H = 60$$ J
Net work done by the system $$W= 15$$ J
Thus efficiency of the system $$\eta = \dfrac{W}{Q_H} = \dfrac{15}{60} =0.25$$
Thus the system is $$25$$% efficient.
Question 4
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Identify which of the following statement does NOT apply to the First Law of Thermodynamics?

A
energy cannot be created

B
energy cannot be transformed from one form to another

C
energy cannot be destroyed

D
the amount of energy within a closed system is constant

Solution

First law of thermodynamics is based on the conservation of energy i.e energy can neither be created nor be destroyed but it can be transformed from one form to another.
Thus option B is correct.
Question 5
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Which of the following option are related with the second law of thermodynamics (law of entropy)?

A
The heat lost by one object must be gained by another object

B
Heat flow naturally from a hotter body to a cooler body

C
Celsius degrees and Kelvin degrees are equivalent

D
Heat can be transformed into work

E
The average kinetic energy of molecules is proportional to temperature

Solution

The second law of thermodynamics says that heat flows 'naturally' from an object at a higher temperature to an object at a lower temperature, and heat doesn’t flow in the opposite direction of its own accord, since the entropy in such a process increases.
The reverse is not possible due to decrease in entropy in such a process.
Question 6
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Directions For Questions

A heat engine is used to produce a mechanical energy from heat energy. If it exhausts 100 J of energy into surrounding and useful work done by it is 50 J.

...view full instructions

The heat added to the heat engine is

A
150 J

B
100 J

C
50 J

D
2J

E
Zero

Solution

Heat added to the system $$Q_a = W + Q_r = 50 + 100 =150$$ $$J$$
Question 7
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Identify the best curve which represents how pressure and volume change in an isothermal process?

A

B

C

D

E

Solution

Ideal gas equation: $$PV = nRT$$
Isothermal process : $$T = constant$$ $$\implies PV = constant$$
Thus P-V graph is a hyperbola.
Hence option A is correct.
Question 8
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An unknown liquid at a high temperature is safely mixed with normal water until an equilibrium temperature is reached. Some heat is gained by the cold water. Identify by which of the following law this can be explained ?

A
First law of thermodynamics (conservation of energy)

B
Second law of thermodynamics (law of entropy)

C
Ideal gas law

D
Heat of fusion and heat of vaporization equation

E
Heat engine efficiency

Solution

According to the law of conservation of energy, the total energy of the system would remain the same.
On addition of hot liquid into the normal water, the hot liquid lost heat energy in order to achieve the equilibrium temperature. The same amount of heat is absorbed by the water to raise its temperature to the equilibrium level.
Question 9
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The first law of thermodynamics is derived from which of the following law ?

A
the law of conservation of energy

B
the law of specific heat

C
the ideal gas law

D
the law of entropy

E
the law of conservation of temperature

Solution

According to 1st law of thermodynamics, $$Q = \Delta U+W$$
$$\implies$$ Energy can neither be created nor be destroyed.
Thus 1st law of thermodynamics is derived from law of conservation of energy.
Question 10
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The basis for measuring thermodynamic property of temperature is given by

A
Zeroth law of Thermodynamics

B
First law of Thermodynamics

C
Second law of Thermodynamics

D
Third law of Thermodynamics

Solution

$$Answer:-$$ A
The zeroth law of thermodynamics states that if two thermodynamic system are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.
Two systems are said to be in the relation of thermal equilibrium if they are linked by a wall permeable only to heat and they do not change over time.
So temperature according to this law was taken as thermodynamic property.
The zeroth law justifies the use of suitable thermodynamic systems as thermometers to provide such a labeling, which yield any number of possible emprical temperature scales.