Thermodynamics Test

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Thermodynamics Test - 21

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Question 1
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When a gas undergoes an adiabatic compression its:

A
temperature decreases

B
temperature increases

C
volume increases

D
pressure decreases

E
energy decreases

Solution

In an adiabatic process , no heat enters or leaves the system i.e. $$dQ=0$$.
The first law of thermodynamics says ,
$$dQ=dU+dW=0$$
or $$dU=-dW$$
when a gas compresses adiabatically , work is done on the system ,therefore $$dW$$ must be negative i.e. change in internal energy is positive it means internal energy of the system would increase and hence the temperature of the gas will increase.
Question 2
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A gas undergoes a reversible adiabatic expansion. Identify the correct option about gas.

A
Energy increases

B
Pressure increases

C
Volume decreases

D
Temperature increases

E
Temperature decreases

Solution

From First Law of Thermodynamics,
$$Q=W+\Delta U$$
For an adiabatic process,
$$Q=0$$
$$\implies W+\Delta U=0$$
$$\implies \Delta U=-W$$
For adiabatic expansion, the work done would be positive.
Hence change in internal energy of system is negative.
Thus internal energy deceases, and so does the temperature.
Question 3
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Which of the following statement is true as per the second law of thermodynamics for an isolated, ordered system?

A
Heat will flow into the system

B
Heat will flow out of the system

C
Work will be done by the system

D
Work will be done on the system

E
The entropy withing the system will increase

Solution

The second law of thermodynamic states that the entropy of an isolated system increases over time and remain constant for reversible process.
Question 4
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Which of the following is true about refrigeration?

A
Heat is removed from the inside of the refrigerator

B
Cold air is produced inside the refrigerator

C
Hot air is removed from the inside of the refrigerator

D
Hot air is changed to a cold condensate inside the refrigerator

E
Hot air inside the refrigerator is expanded to remove its heat

Solution

A refrigerator is infact a reverse heat engine which absorbs heat from source (material) at lower temperature, do work on it and then passes the heat to the sink (sorrounding) at higher temperature, thus we can say that heat is removed from inside the refrigerator.
Question 5
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Which of the following is a restatement of first law of thermodynamics:

A
Guy-Lassac's Law

B
The principle of entropy

C
The principle of enthalpy

D
Conservation of energy

E
Avogadro's hypothesis

Solution

First law of thermodynamics states that the quantity of heat given to a system $$dQ$$ is equal to the sum of the increase in its internal energy $$dU$$ and the external work done by the system $$dW$$ in expansion
$$dQ=dU+dW$$
it means total energy is conserved there is no loss of energy
Question 6
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Identify which of the following is correct about the cooling process as shown above ?
I. Negative work
II. An isothermal process
III. Increasing energy

A
I only

B
II only

C
I and III only

D
II and III only

E
I, II, and III

Solution

Here the arrow of work input towards the cooling device so its means work on the system. We know that work on the system will be negative. In this process, temperature is increasing so its not a isothermal and it is increasing energy. Thus, statement I will be right.
Question 7
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A heat engine receives $$150$$ Joules of heat energy and performs $$70$$ Joules of work. If heat loss in the surrounding is zero. Find out by what value does the internal energy of the system change?

A
$$0 J$$

B
$$40 J$$

C
$$80 J$$

D
$$120 J$$

E
$$150 J$$

Solution

By the first law of thermodynamics, $$dQ=dU+W$$
so, change in internal energy $$dU=dQ-W=150-70=80 J$$
Question 8
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Which of the following option hold true for the above heat engine?

A
Positive work

B
An adiabatic process

C
An isobaric process

D
An isochoric process

E
An isothermal process

Solution

As the heat is absorbed by heat engine from source (hot reservoir) then it give some heat into work and rest is given to the sink(cold reservoir) so ($$Q_{1}>Q_{2}$$). Therefore net work done $$W=Q_{1}-Q_{2}$$ will be positive.
Question 9
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Identify the incorrect statement ?

A
Energy can be converted into matter

B
Matter can be converted into energy

C
Energy can be converted into matter, and matter can be converted into energy

D
Matter can be converted into energy, but energy cannot be converted into matter

E
Energy can be measured in units of joules and calories

Solution

Energy and matter are interconvertible and the relation between them is given by $$E=mc^2$$ as followed from Einstein's theory of Relativity.
The conversion of energy, kinetic or electromagnetic, to particles with rest mass is experimentally observed only when the energy comes in big enough clumps to create a massive particle, when the energy is low, this is going to be the lightest charged particle, the electron. Electrons can only be created along with a positively charged particle, to conserve charge, and this is almost always a positron.
The conversion of mass to energy is nowadays popular in nuclear fission reactors.
Question 10
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During what kind of process is there no change in internal energy?

A
adiabatic

B
isothermal

C
isobaric

D
cyclic (one cycle)

E
Two of the answers are correct.

Solution

Isothermal process : $$T = constant$$ i.e $$\Delta T = 0$$ K
Change in internal energy $$\Delta U = nC_v (\Delta T) = 0$$ J
Thus internal energy remains constant in an isothermal process.
As internal energy is a state function, thus change in internal energy is also zero in one cycle of a cyclic process.
Hence option E is correct.

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Thermodynamics Test - 21

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Thermodynamics Test - 21

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Question 1

temperature decreases

temperature increases

volume increases

pressure decreases

energy decreases

Solution

Question 2

Energy increases

Pressure increases

Volume decreases

Temperature increases

Temperature decreases

Solution

Question 3

Heat will flow into the system

Heat will flow out of the system

Work will be done by the system

Work will be done on the system

The entropy withing the system will increase

Solution

Question 4

Heat is removed from the inside of the refrigerator

Cold air is produced inside the refrigerator

Hot air is removed from the inside of the refrigerator

Hot air is changed to a cold condensate inside the refrigerator

Hot air inside the refrigerator is expanded to remove its heat

Solution

Question 5

Guy-Lassac's Law

The principle of entropy

The principle of enthalpy

Conservation of energy

Avogadro's hypothesis

Solution

Question 6

I only

II only

I and III only

II and III only

I, II, and III

Solution

Question 7

$$0 J$$

$$40 J$$

$$80 J$$

$$120 J$$

$$150 J$$

Solution

Question 8

Positive work

An adiabatic process

An isobaric process

An isochoric process

An isothermal process

Solution

Question 9

Energy can be converted into matter

Matter can be converted into energy

Energy can be converted into matter, and matter can be converted into energy

Matter can be converted into energy, but energy cannot be converted into matter

Energy can be measured in units of joules and calories

Solution

Question 10

adiabatic

isothermal

isobaric

cyclic (one cycle)

Two of the answers are correct.

Solution

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