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HUMIDITY

Water vapour is always present in the air to a greater or lesser extent, in the
troposphere
...

Water evaporates into the air from oceans, lakes, rivers, vegetation etc
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The water cycle is thus completed
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Air that contains no water vapour is called dry air
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Moist Air
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It is also called
unsaturated or dry air at the existing temperature and pressure
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Air is like,a, sponge which can_absorb certain amount of water and
no more When the air holds maximum water vapour, it is called saturated air
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The partial pressure exerted by water vapour in the air is called vapour pressure
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Saturation Vapour Pressure
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It is defined as the actual amount of water vapoursontained in a
given volume of air at a given temperature
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Humidity Mixing Ratio
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It is expressed as g/kg
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It is defined as the maximum mass of
water vapour that can be contained in a given mass of air at a particular temperature
and pressure
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It is defined as the ratio, in percentage, of the _actual water
vapour present in the air to the maximum it can contain at the same temperature and
pressure
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) It is the lowest temperature which air would
attain by evaporating water into it to saturate it
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Dryer the air more effective would be the cooling
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Cooling below Dew
Point (DP) causes condensation
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Various terms used for describing water
content in the atmosphere are:
QUESTIONS ON HUMIDITY
Q1
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The temperature to which air be cooled at constant pressure to become
saturated, is called
(a) Wet bulb temperature
(b) Dry bulb temperature
(c) Dew point
(d) Humidity
Q3
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On a rainy day compared to sunny day the length of runway required is
(a) More
(b) Less
(c) Same
Q5
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During a night with a clear sky, surface temperature will
RH will
and Dewpoint will
a)Fall, Rise, Rise
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c)Fall, Rise, Remain the same
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A change of state directly from a solid to a vapour or vice versa is:
a)insolation
b)condensation
c)evaporation
d)sublimation
4
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The process of change of state from a gas to a liquid is:
a)evaporation in which latent heat is absorbed
b)evaporation in which latent heat is released
c)condensation in which latent heat is absorbed
d)condensation in which latent heat is released
6
...
The saturation vapour pressure over water is than the ice
(a) More
(b) Less
(c) Same
Q7
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Air is classified as dry or saturated according to its relative humidity
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On a wet bulb thermometer in an unsaturated atmosphere there will be a
reduction of temperature below that of the dry bulb thermometer because:
a) heat is absorbed during the process of condensation
b) heat is released during the process of condensation
c) heat is absorbed by the thermometer during the process of evaporation
d) heat is released from the thermometer during the process of evaporation
Q10
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Absolute humidity is:
a) The number of water droplets in a given quantity of air
b) The amount of water vapour that a given quantity of air holds
c) The maximum amount of water vapour that a given quantity of air can hold
d) The maximum number of water droplets that a given quantity of air can hold
Q11
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The wet bulb temperature:
a ) i s m e a s u r e d u s i n g a h y dr o m et er
b ) is the minimum temperature to which a thermometer bulb can be cooled by
the evaporation of water
c ) me asur es t he dew po int o f t he air
d ) is the minimum temperature reached by the surface of the earth as measured by a
thermometer placed 1
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Which one of the following statements relating to atmospheric humidity is

correct:
a)
b)
c)
d)

If the air temperature falls then the absolute humidity must increase
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The diurnal variation of dewpoint temperature is greatest when skies are clear at
night
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Q14
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greater; absorbed
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lesser; absorbed
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When water vapour changes to ice:
a)
b)
c)
d)

Latent heat is absorbed
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Latent heat is released
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Q16
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Humidity Mixing Ratiowhen air is lifted adiabatically
(a) decreases
(b) remains constant
(c) increases
Q18
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(a) Wet bulb temp
(b) Dry bulb temp
(c) Dew point



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