The latent heat of vaporisation of a substance is always fr

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 Multiple Choice QuestionsMultiple Choice Questions

151.

What is the slope for an isothermal process?

  • PV

  • - PV

  • Zero


152.

For an adiabatic process

  • ΔS = 0

  • Δu = 0

  • Q = 0

  • W = 0


153.

For cyclic process which of the following quantity is zero? 

  • ΔV

  • Δu

  • W

  • ΔQ


154.

Assertion:  During rapid pumping of air in tyres, air inside the tyre is hotter than atmospheric air.

Reason:  Adiabatic process occurs at very high rate.

  • If both assertion and reason are true and reason is correct explanation of assertion.

  • If both assertion and reason are true but reason is not correct explanation of assertion. 

  • If assertion is true but reason is false.

  • If both assertion and reason are false.


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155.

The latent heat of vaporisation of a substance is always

  • greater than its latent heat of fusion

  • greater than its latent heat of sublimation

  • equal to its latent heat of sublimation

  • less than its latent heat of fusion


A.

greater than its latent heat of fusion

Heat of vaporization: The heat of vaporization of water is defined as the amount of heat needed to turn 1 g of liquid into vapor.

Heat of fusion:- It is the energy needed to one gram of a liquid to vaporize ( boil ) without a change in pressure.

The energy required to completely separate the molecules ( in case of vaporization), i.e to convert the liquid into gas, is much greater than if you were  just to reduce their separation, solid to liquid separation, solid to liquid. Hence the reason is why the latent heat of vaporization is greater than the latent heat of fusion.  More energy is needed to completely separate molecules having large distance from each other.


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156.

A reversible engine converts one-sixth of the heat input into work. When the temperature of the sink is reduced by   62°C, the efficiency of the engine is doubled. The temperatures of the source and sink are

  • 99oC, 37oC

  • 80oC, 37oC

  • 95oC, 37oC

  • 90oC, 37oC


157.

Graph of specific heat at constant volume for a monoatomic gas is

  •  

  •  


158.

Assertion:  Water kept in an open vessel will quickly evaporate on the surface of the moon. 

Reason:  The temperature at the surface of the moon is much higher than boiling point of water.

  • If both assertion and reason are true and reason is the correct explanation of assertion.

  • If both assertion and reason are true but reason is not the correct explanation of assertion.

  • If assertion is true but reason is false.

  • If both assertion and reason are false.


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159.

Assertion:  For  an  isothermal  process  in  an  ideal  gas,  the heat  obsorbed  by the  gas is  entirely  used   in  the  work  done  by  the  gas. 

Reason:  During  a  process  taking  place in  a  system, the temperature remains constant then the  process is isothermal.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


160.

A slab consists of two layers of different materials of the same thickness and having thermal conductivities  K1 and K2  are connected in series. The equivalent thermal conductivity of the slab is

  • 2 K1 K2K1 + K2

  • K1 K2

  • K1 K2K1 + K2

  • K1 + K2


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