EWT | Academic Question

Questions
Question (1)
QN0038438

The first operation involved in a Carnot cycle is

  • (A)

    isothermal expansion

  • (B)

    adiabatic expansion

  • (C)

    isothermal compression

  • (D)

    adiabatic compression

Correct Answer: A
Explanation:

First operation in carnot cycle is isothermal expansion.

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Question (2)
QN0038439

Which of the following statements is incorrect?

  • (A)

    All reversible cycles have same efficiency

  • (B)

    Reversible cycle has more efficiency than an irreversible one

  • (C)

    Carnot cycle is a reversible one

  • (D)

    Carnot cycle has the maximum efficiency in all cycles

Correct Answer: A
Explanation:

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Question (3)
QN0038440

A Carnot engine works between a source and a sink maintained at constant temperatures  and . 

       For efficiency to be the greatest        

  • (A)

    and  should be high

  • (B)

    and  should be low

  • (C)

    should be low and  should be high

  • (D)

    should be high and  should be low

Correct Answer: D
Explanation:

So for  be high  must be high and  must be low:

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Question (4)
QN0038441

The efficiency of a Carnot engine operating between the temperatures of  and  will be

  • (A)

  • (B)

  • (C)

  • (D)

Correct Answer: D
Explanation:

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Question (5)
QN0038442

The temperature of source and sink of a heat engine are  and  respectively. An inventor 

claims its efficiency to be , then:      

  • (A)

    it is impossible

  • (B)

    it is possible with high probability

  • (C)

    it is possible with low probability

  • (D)

    data are insufficient.

Correct Answer: A
Explanation:

Hence, it is not possible to have efficiency more than .

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Question (6)
QN0038443

Even Carnot engine cannot give  efficiency because we cannot

  • (A)

    prevent radiation

  • (B)

    find ideal sources

  • (C)

    reach absolute zero temperature

  • (D)

    eliminate friction

Correct Answer: C
Explanation:

Absolute zero temperature is practically not reachable.

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Question (7)
QN0038444

 If the temperatures of source and sink of a Carnot engine having efficiency  are each decreased 

by , then the efficiency       

  • (A)

    remains constant

  • (B)

    becomes 1 .

  • (C)

    decreases

  • (D)

    increases

Correct Answer: D
Explanation:

Efficiency,

.

Comparing with  we get, the efficiency increases.

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Question (8)
QN0038445

A Carnot engine takes  cal. of heat from a reservoir at , and gives it to a sink at . 

The work done by the engine is

  • (A)

  • (B)

  • (C)

  • (D)

    zero

Correct Answer: B
Explanation:

work  Heat

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Question (9)
QN0038446

A diatomic ideal gas is used in a car engine as the working substance. If during the adiabatic expansion 

part of the cycle, volume of the gas increases from  to , the efficiency of the engine is

  • (A)

    0.5

  • (B)

    0.75

  • (C)

    0.99

  • (D)

    0.25

Correct Answer: B
Explanation:

The efficiency of cycle is

For adiabatic process

constant

For diatomic gas 

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Question (10)
QN0038447

 A Carnot engine operating between temperatures and  has efficiency . When  is lowered by  

its efficiency increases to . Then  and  are, respectively        

  • (A)

    and 

  • (B)

    and 

  • (C)

    and 

  • (D)

    and 

Correct Answer: D
Explanation:

On solving Eqs. (i) and (ii)

and

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