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    Thermodynamics
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    A gas is compressed from volume V1 to V.2  In which case work done will be more-isothermal compression or adiabatic compression?
    The PV curve for isothermal and adiabatic compression is as shown in figure.
    The PV curve for isothermal and adiabatic compression is as shown in
    We know that the area under PV graph is equal to work done on the gas. Thus, the work done on gas during adiabatic compression is maximum and isobaric compression is minimum.
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    What is the relative humidity of air when the room temperature is 16°C and the dew point is 7.4°C? Given that the saturated vapour pressure at 7°C, 8°C and 16°C is 7.5mm, 8mm and 13.5mm respectively of mercury.

    Given,

    Room temperature, T = 16°C

    Dew point temperature, T0 = 7.4°C

    SVP at 7°C = 7.5mm of Hg

    SVP at 8°C = 8mm of Hg

    SVP at 16°C = 13.5mm of Hg

    For a small change in temperature, it can be assumed that saturated vapour pressure changes linearly.

    The saturated vapour pressure increases by 0.5 mm for one degree rise in temperature.

    Therefore increase in saturated vapour pressure for 0.4°C increase in temperature will be 0.2mm of mercury.

    Hence, the saturated vapour pressure at dew point i.e. 7.4°C is 7.7 mm of mercury.

    Now the relative humidity is,

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    A gas expands from volume V1 to V2. In which case work done will be more: isothermal expansion, isobaric expansion or adiabatic compression?

    The PV curve for isothermal, isobaric and adiabatic compression is as shown in figure.
    The PV curve for isothermal, isobaric and adiabatic compression is as
    We know that the area under PV graph is equal to work done by the gas. Thus the work done by gas during isobaric expansion is maximum and adiabatic expansion is minimum.
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    If the gas loses heat without doing any work, then what type of process is it?
    Gas is not doing any work therefore the volume of gas remains constant during the process. Hence, the process is an isochoric process.

    Since the gas loses heat, therefore temperature of the gas will fall. 
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    Air in a cylinder, is suddenly compressed to half of its initial volume by a piston which is then maintained at that new position. What happens to the pressure of gas with the passage of time?
    Sudden compression is an adiabatic compression.

    Thus, just after compression, the pressure of gas increases to 2    γP which is greater than the initial pressure. The temperature increases to 2γ–1 T, which is greater than T. 

    Here, 

    P is the initial pressure, and 
    T is the initial temperature. 

    With the passage of time, the temperature of air starts decreasing due to loss of heat to the surrounding. This results in the decrease of pressure at constant volume. Finally the pressure of air decreases to 2P. 
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