Thermodynamics Test

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Thermodynamics Test - 8

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Weekly Quiz Competition

Question 1
1 / -0

In a heat engine the ratio of net work done per cycle by the engine to the total amount of heat absorbed per cycle by the working substance from the source is known as

A
Adiabatic compression ratio

B
Specifie heat ratio

C
conductivity

D
Thermal Efficiency

Solution

In a heat engine the ratio of net work done per cycle by the engine to the total amount of heat absorbed per cycle by the working substance from the source is known as Thermal Efficiency.
Question 2
1 / -0

In actual home refrigerator vapours of Freon ( which is dichlorodifluoro methane CCl₂F₂) act as

A
Sink

B
working substance

C
source

D
Insulating pad

Solution

Dichlorodifluoromethane (R-12) is a colorless gas usually sold under the brand name Freon-12, and a chlorofluorocarbon halomethane (CFC) used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was banned in developed countries (non-article 5 countries) in 1996, and developing countries (article 5 countries) in 2010 due to concerns about its damaging impact to the ozone layer.[better source needed] Its only allowed usage is as fire retardant in submarines and aircraft. It is soluble in many organic solvents. Dichlorodifluoromethane was one of the original propellants for Silly String. R-12 cylinders are colored white.
Question 3
1 / -0

A carnot engine is taking 700 cal from source and is rejecting 500 cal to the sink in each cycle. What is the temperature of sink if the source temperature is 150° C .

A
29.02° C

B
27.75° C

C
30.05° C

D
31.5° C

Solution

Heat extracted from source Q1= 700 cal
Heat rejected to the sink Q2= 500 cal
Temperature of source T1= 150 +273= 423K
Temperature of sink T2 to be found:
Q2/Q1 = T2/T1
So,
T2 = (Q2/Q1) x T1
= (500 x 423)/700
= 302.02 K
= 29.02 degree C.
Question 4
1 / -0

According to Carnot theorem no heat engine working between two given temperatures of source and sink can be more efficient than a perfectly ___________ engine working between the same two temperatures

A
Reversible

B
Heat

C
Ideal gas

D
Combustible

Solution

According to Carnot theorem no heat engine working between two given temperatures of source and sink can be more efficient than a perfectly reversible engine working between the same two temperatures, by the statement of Carnot theorem.
Question 5
1 / -0

How much heat energy a petrol engine would require to do 20 kWh of work? Its adiabatic compression ratio is 9 and γ= 1.5.

A
10.7 J

B
30 J

C
1.07 X10⁷J

D
180 J

Solution
Question 6
1 / -0

An ideal gas undergoes four different processes from the same initial state (Fig.). Four processes are adiabatic, isothermal, isobaric and isochoric. Out of 1, 2, 3 and 4 which one is adiabatic.

A
4

B
3

C
1

D
2

Solution

4 is isobaric process, 1 is isochoric. Out of 3 and 2, 3 has the smaller slope (magnitude) hence is isothermal. Remaining process 2 is adiabatic.
Question 7
1 / -0

What would be the horse power of a steam engine with average pressure of steam 9x 10⁴ Nm^-2 , the area of cross section of the piston is 0.2 m², length of stroke is 0.6 m and piston makes 5 revolutions per second?

A
150 h.p.

B
140.7 h.p.

C
104.7 h.p.

D
144.77 h.p.

Solution

Energy in 1 revolution=2 x P x a x l=2 x 9 x104 x 0.2 x0.6 j=21600J
Energy in n revolutions= 21600nJ
Power=E/t=21600n/t=21600 x 5=18000 J/s= 108000/746 h.p=144.77 h.p.
Question 8
1 / -0

The ratio of quantity of heat removed per cycle from the contents of the refrigerator to the energy spent per cycle to remove this heat is called the

A
coefficient of performance

B
principle of heat engine

C
efficiency of heat engine

D
efficiency of refrigerator

Solution

The ratio of quantity of heat removed per cycle from the contents of the refrigerator to the energy spent per cycle to remove this heat is called the coefficient of performance. It is the definition of coefficient of performance.
Question 9
1 / -0

In a Carnot engine 800 J of heat is absorbed from a source at 400 K and 640 J of heat is rejected to the sink. The temperature of the sink is:

A
273 K

B
100 K

C
320 K

D
240 K

Solution

for hot reservoir I.e. source
temperature T₁=400k
heat supplied Q₁=800J
For cold reservoir i.e. sink
Temperature T₂=?
Heat supplied Q₂=640J
According to carnot’s theorem,
Q₁/Q₂= T₂/T₁
640/800= T₂/400
T₂=320k
Question 10
1 / -0

The temperature inside a refrigerator is 4°C and the room temperature is 27°C. How many joules of heat will be delivered to the room for each joule of electricity consumed by the refrigerator?( Treat the refrigerator as ideal).

A
1 J

B
12 J

C
8.3 J

D
13 J

Solution

Coefficient of performance(cop) of a refrigerator,
β= Q₂/Q₁-Q₂=T₂/T₁-T₂=277/300-277=277/23≈12
OR, Q₂/W=12. Therefore, W=1J.Q₂=12J
Also, Q1=Q2+W
=(12+1) J
=13J

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Thermodynamics Test - 8

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Thermodynamics Test - 8

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Question 1

Adiabatic compression ratio

Specifie heat ratio

conductivity

Thermal Efficiency

Solution

Question 2

Sink

working substance

source

Insulating pad

Solution

Question 3

29.02° C

27.75° C

30.05° C

31.5° C

Solution

Question 4

Reversible

Heat

Ideal gas

Combustible

Solution

Question 5

10.7 J

30 J

1.07 X107 J

180 J

Solution

Question 6

4

3

1

2

Solution

Question 7

150 h.p.

140.7 h.p.

104.7 h.p.

144.77 h.p.

Solution

Question 8

coefficient of performance

principle of heat engine

efficiency of heat engine

efficiency of refrigerator

Solution

Question 9

273 K

100 K

320 K

240 K

Solution

Question 10

1 J

12 J

8.3 J

13 J

Solution

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1.07 X10⁷J