Thermodynamics Test

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Thermodynamics Test - 27

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following is not the component of heat pump?

A
Condenser

B
Compressor

C
Cooler

D
Expansion valve

Solution

A heat pump is a device that transfers heat energy from a source of heat to what is called a "heat sink". Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses a small amount of external power to accomplish the work of transferring energy from the heat source to the heat sink,there are four main components of heat pump: compressor, condenser, expansion valve and evaporator
Question 2
1 / -0

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

Solution

The adiabatic condition is given by the relation between pressure volume and temperature volume as:

$$PV^\gamma=$$ constant and $$TV^{\gamma-1}=$$ constant
where, $$\gamma=\dfrac{C_p}{C_v}$$ is ratio of the specific heats
These relations suggest that an decrease in volume is associated with increase in temperature and pressure.
Question 3
1 / -0

The earthen pots prepared by using clay only are generally

A
Porous

B
Non-porous

C
Conductors of electricity

D
Transparent

Solution

The earthen pots prepared by using clay only are generally porous to facilitate cooling process.This works through evaporative cooling. Capillary action causes water to seep and evaporate from the mini-pores in the pot, taking the heat from the water inside, thus making the water inside cooler than the outside temperature.
Question 4
1 / -0

A heat engine undergoes a process in which its internal energy decreases by $$400 J$$ and it gives out $$150 J$$ of heat. During the process

A
It does $$250 J$$ of work and its temperature rises

B
It does $$250 J$$ of work and its temperature falls

C
It does $$550 J$$ of work and its temperature rises

D
It does $$550 J$$ of work and its temperature falls

Solution

The internal energy of the system will decrease when the system does work and/or gives off heat. Since the heat given out is 150 J and the reduction in internal energy is 400 J, the work done by the engine is 400– 150 = 250 J.
When the internal energy is reduced, the system is cooled. Therefore, temperature will decrease.
Question 5
1 / -0

In a given process on an ideal gas $$dW = 0$$ and $$dQ < 0$$, then for the gas :

A
The temperature will decrease

B
The volume will increase

C
The pressure will remain constant

D
The temperature will increase

Solution

From first law of thermodynamics,
$$dQ=dU+dW$$
we have $$dQ=dU$$ $$\left( as\quad dW=0 \right) $$
But $$dQ < 0$$
$$\therefore dU < 0$$
$$N{ C }_{ V }\Delta T< 0$$
or $$\Delta T < 0$$
Hence, the temperature will decrease.
Question 6
1 / -0

Find out the most efficient engine in the following

A
An engine converts 80 KJ of heat energy into 20 KJ of work

B
An engine converts 50 KJ of heat energy into 15 KJ of work

C
An engine converts 30 KJ of heat energy into 6 KJ of work

D
An engine converts 60 KJ of heat energy into 24 KJ of work

Solution

Efficiency of heat engine= $$\frac{work done}{heat input}$$ Going by the above options efficiency is maximum in option D, and is equal to 40 percent.
Question 7
1 / -0

Which of the following engines is more efficient?

A
Heat utilised - 80 kilojoules , work done - 32 kilojoules

B
Heat utilised - 60 kilojoules , work done - 12 kilojoules

C
Heat utilised - 50 kilojoules , work done - 25 kilojoules

D
Heat utilised - 90 kilojoules , work done - 27 kilojoules

Solution

Efficiency of engine $$\eta = \dfrac{W}{Q_H}$$
where $$W$$ is work done and $$Q$$ is heat taken from source (Heat utilised)
(A) : $$\eta_A = \dfrac{32}{80} = 0.4$$
(B) : $$\eta_B = \dfrac{12}{60} = 0.2$$
(C) : $$\eta_C = \dfrac{25}{50} = 0.5$$
(D) : $$\eta_D = \dfrac{27}{90} = 0.3$$
Hence engine C is the most efficient.
Question 8
1 / -0

Of the following thermodynamic processes, the thermodynamic process in which internal energy of a gas remains constant is

A
adiabatic

B
isochoric

C
isobaric

D
isothermal

Solution

An isothermal process is a change of a system, in which the temperature remains constant: $$ΔT = 0$$. This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change will occur slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange. In contrast, an adiabatic process is where a system exchanges no heat with its surroundings ($$Q = 0$$). In other words, in an isothermal process, the value $$ΔT = 0 $$and therefore $$ΔU = 0$$ (only for an ideal gas) but $$Q ≠ 0$$, while in an adiabatic process, $$ΔT ≠ 0$$ but $$Q = 0$$.
Question 9
1 / -0

The first law of thermodynamics is a special case of

A
Newton's law

B
Stefan's law

C
the law of heat excahange.

D
the law of consevation of energy.

Solution
Question 10
1 / -0

The Zeroth law of thermodynamics leads to the concept of:

A
internal energy

B
heat content

C
pressure

D
temperature

E
work done

Solution

Explanation:
The Zeroth Law of Thermodynamics: It states that if two bodies are each in thermal equilibrium with some third body, then they are also in equilibrium with each other. Thermal equilibrium means that two bodies have same temperature.
So Zeroth Law of Thermodynamics leads to the concept of temperature.
So option $$D$$ is correct.

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Thermodynamics Test - 27

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Thermodynamics Test - 27

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Question 1

Condenser

Compressor

Cooler

Expansion valve

Solution

Question 2

increase in temperature and decrease in pressure

decrease in temperature and increase in pressure

decrease in temperature and decrease in pressure

increase in temperature and increase in pressure

Solution

Question 3

Porous

Non-porous

Conductors of electricity

Transparent

Solution

Question 4

It does $$250 J$$ of work and its temperature rises

It does $$250 J$$ of work and its temperature falls

It does $$550 J$$ of work and its temperature rises

It does $$550 J$$ of work and its temperature falls

Solution

Question 5

The temperature will decrease

The volume will increase

The pressure will remain constant

The temperature will increase

Solution

Question 6

An engine converts 80 KJ of heat energy into 20 KJ of work

An engine converts 50 KJ of heat energy into 15 KJ of work

An engine converts 30 KJ of heat energy into 6 KJ of work

An engine converts 60 KJ of heat energy into 24 KJ of work

Solution

Question 7

Heat utilised - 80 kilojoules , work done - 32 kilojoules

Heat utilised - 60 kilojoules , work done - 12 kilojoules

Heat utilised - 50 kilojoules , work done - 25 kilojoules

Heat utilised - 90 kilojoules , work done - 27 kilojoules

Solution

Question 8

adiabatic

isochoric

isobaric

isothermal

Solution

Question 9

Newton's law

Stefan's law

the law of heat excahange.

the law of consevation of energy.

Solution

Question 10

internal energy

heat content

pressure

temperature

work done

Solution

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