Thermodynamics Test

Result

Thermodynamics Test - 46

Score
-
out of -
Rank
-
out of -

TIME Taken - -

SHARING IS CARING

If our Website helped you a little, then kindly spread our voice using Social Networks. Spread our word to your readers, friends, teachers, students & all those close ones who deserve to know what you know now.

Weekly Quiz Competition

Question 1
1 / -0

In above shown figure of refrigeration system. Which of the following statement explains why work is an input into this system?

A
Work is needed to move thermal energy against temperature gradient.

B
Work is needed to reduce the amount of thermal energy lost during transfer.

C
Work uses energy from the cold reservoir to reduce the temperature of the system.

D
Work adds energy to the cold reservoir to increase the heat flow to the hot reservoir.

E
Work adds heat to the system, causing the temperature of both reservoirs to increase.

Solution

In a thermodynamic system, heat naturally flows from hotter body to a colder body. The given figure shows a refrigerator energy flow diagram. The heat flow is opposite to the direction of conventional heat flow and hence external work is required for the given heat flow diagram.
Question 2
1 / -0

In a thermodynamic processes during each cycle , a heat engine absorbs 400 J of heat from a higher- temperature source and release 300 J of heat to the low-temperature sink. Calculate the efficiency of heat engine?

A
$$\dfrac{1}{7}$$

B
$$\dfrac{1}{4}$$

C
$$\dfrac{3}{7}$$

D
$$\dfrac{4}{7}$$

E
$$\dfrac{3}{4}$$

Solution

The efficiency of heat engine, $$\eta=\dfrac{W}{Q_1}=\dfrac{Q_1-Q_2}{Q_1}=\dfrac{400-300}{400}=1/4$$
Question 3
1 / -0

A heat engine takes in heat at 750 degrees Celsius and expels heat at 250 degrees Celsius. What is this engine's theoretically ideal (Carnot) efficiency?

A
33 percent

B
67 percent

C
49 percent

D
300 percent

E
23 percent

Solution

Temperature of source $$T_H = 750^oC = 750+273 = 1023$$ K
Temperature of sink $$T_L = 250^oC = 250+273 = 523$$ K

Efficiency of engine $$\eta = 1-\dfrac{T_L}{T_H} = 1 -\dfrac{523}{1023} =0.49$$
Thus the engine is $$49$$% efficient.
Question 4
1 / -0

Find out the efficiency of the heat engine if it produces $$100 J$$ of heat, does $$30 J$$ of work, and emits $$70 J$$ into a cold reservoir.

A
$$100$$%

B
$$70$$%

C
$$42$$%

D
$$40$$%

E
$$30$$%

Solution

Efficiency of a heat engine is given by ,
$$\eta=\dfrac{W}{Q_{1}}$$
where $$W=$$ net work done /cycle and $$Q_{1}=$$total heat absorbed / cycle
given - $$W=30J$$ , $$Q_{1}=100J$$
therefore $$\eta=\dfrac{30}{100}\times100=30$$%
Question 5
1 / -0

A heat engine produces 100 J of heat, does 30 J of work, and emits 70 J into a cold reservoir. What is the efficiency of the heat engine?

A
100%

B
70%

C
42%

D
40%

E
30%

Solution

The efficiency of heat engine is $$\eta=\dfrac{W}{Q_{in}}$$
Here work done , $$W=30 J$$ and heat produced $$Q_{in}=100 J$$
Thus, % of efficiency, $$\eta=\dfrac{30}{100}\times 100=30$$ %
Question 6
1 / -0

The idealized P-V diagram above shows a complete cycle through compression and expansion of a gas. The questions below relate to the processes within the cycle.
Which letter shows work done?

A
A

B
B

C
C

D
D

E
E

Solution

Here the work done will be the area under the pressure-volume curve. The work done under the part A will be positive work, but the negative work done under the part C must be subtracted. Thus the leaving work as E as shown in diagram. Thus, option E will be correct.
Question 7
1 / -0

During a cyclic thermodynamic process, a gas absorbs 45 J of heat.
Which table correctly describes the change in internal energy in the gas and work done by the gas during this cycle?

A
$$45 $$ $$J$$

B
$$54 $$ $$J$$

C
$$40 $$ $$J$$

D
$$50 $$ $$J$$

E
$$60 $$ $$J$$

Solution

As heat is absorbed by the gas, $$\implies$$ $$Q = + 45$$ J
Change in internal energy of the gas during one cycle is zero i.e $$\Delta U =0$$ J
From 1st law of thermodynamics : $$Q = \Delta U + W$$
$$\therefore$$ $$45 = 0+ W$$ $$\implies W = +45$$ J
Thus the work done by the gas is $$45$$ J.
Question 8
1 / -0

The thermal capacity of $$10$$gm of the substance is $$8$$ calories. Then its specific heat is.

A
$$0.8$$

B
$$1.25$$

C
$$0.4$$

D
$$0.1$$

Solution

thermal capacity=specific heat *mass, mass=density*volume.
specific heat =$$\dfrac{Thermal.capacity}{mass}=\dfrac{8}{10}=0.8$$
Question 9
1 / -0

For a particular heat engine, 3,000 J of energy goes in at 700 K and 2000 J comes out at 200 K. The rest of the energy is used work.
What is the actual efficiency of this engine?

A
0.71

B
0.33

C
0.67

D
0.29

E
1.5

Solution

Amount of heat goes in the engine $$Q_H = 3000$$ J
Amount of heat rejected by the engine $$Q_R = 2000$$ J
Thus work done by the engine $$W = Q_H - Q_R =3000 - 2000 = 1000$$ J

Actual efficiency of heat engine $$\eta = \dfrac{W}{Q_H} = \dfrac{1000}{3000} = 0.33$$
Question 10
1 / -0

A liquid is being converted into vapours at its boiling point the specific heat of the liquid at this temperature will be.

A
Zero

B
Infinite

C
Positive

D
Negative

Solution

The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure. Therefore, at boiling point, specific heat of a liquid is equal to the specific heat of vaporization of that liquid.

User

Question Analysis

Correct -
Wrong -
Skipped -

My Perfomance

Score
-
out of -
Rank
-
out of -

Re-Attempt Weekly Quiz Competition

Thermodynamics Test - 46

Result

Thermodynamics Test - 46

Score

-

Rank

-

SHARING IS CARING

Question 1

Work is needed to move thermal energy against temperature gradient.

Work is needed to reduce the amount of thermal energy lost during transfer.

Work uses energy from the cold reservoir to reduce the temperature of the system.

Work adds energy to the cold reservoir to increase the heat flow to the hot reservoir.

Work adds heat to the system, causing the temperature of both reservoirs to increase.

Solution

Question 2

$$\dfrac{1}{7}$$

$$\dfrac{1}{4}$$

$$\dfrac{3}{7}$$

$$\dfrac{4}{7}$$

$$\dfrac{3}{4}$$

Solution

Question 3

33 percent

67 percent

49 percent

300 percent

23 percent

Solution

Question 4

$$100$$%

$$70$$%

$$42$$%

$$40$$%

$$30$$%

Solution

Question 5

100%

70%

42%

40%

30%

Solution

Question 6

A

B

C

D

E

Solution

Question 7

$$45 $$ $$J$$

$$54 $$ $$J$$

$$40 $$ $$J$$

$$50 $$ $$J$$

$$60 $$ $$J$$

Solution

Question 8

$$0.8$$

$$1.25$$

$$0.4$$

$$0.1$$

Solution

Question 9

0.71

0.33

0.67

0.29

1.5

Solution

Question 10

Zero

Infinite

Positive

Negative

Solution

User

Question Analysis

My Perfomance

Score