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Dew point and humidity - class-X

Description: dew point and humidity
Number of Questions: 15
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Tags: heat physics
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The most comfortable value for Relative Humidity is

dew point and humidity heat physics

  1. 10%

  2. 20%

  3. 50%

  4. 90%

Show answer
Correct Option: C
Explanation:

50% 

because in this case it won't be too dry or wont be too wet.

The most comfortable value for RH is ______.

dew point and humidity heat physics

  1. 10%

  2. 30%

  3. 50%

  4. 90%

Show answer
Correct Option: C
Explanation:
The most comfortable of RH is 50%,because of this value many environmental
problems can be reduced which include
Mildew
Mold
Bacteria
Condensation

At dew point. Relative Humidity is

dew point and humidity heat physics

  1. 10%

  2. 20%

  3. 50%

  4. 100%

Show answer
Correct Option: D
Explanation:

Dew point is when air gets saturated i.e RH =100%

If RH is high:

dew point and humidity heat physics

  1. we feel sultry

  2. we perspire less

  3. clothes do not dry easily

  4. all the above are correct

Show answer
Correct Option: D
Explanation:
If the air is at 100 percent relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high.

The units of Relative Humidity are

dew point and humidity heat physics

  1. $kg-m^{3}$

  2. kg

  3. $kg-m^{2}$

  4. none of these

Show answer
Correct Option: D
Explanation:

Relative humidity refers to the ratio of the amount of moisture in the air at a certain temperature to the maximum amount of moisture that the air can retain at the same temperature. Relative humidity is expressed as a percentage and is highest during rain.

Write the correct alternatives :
The vapour content in the air is measured using  a physical quantity called...............

dew point and humidity heat physics

  1. Absolute humidity

  2. Relative humidity

  3. Dew point

  4. Humidity

Show answer
Correct Option: B
Explanation:

Relative humidity :

The ratio of the amount of water vapour actually present in the air to the greatest amount possible at the same temperature.
$\therefore$ option $"B"$ is correct.

When it is raining, the dew point is

dew point and humidity heat physics

  1. $0^\circ C$

  2. $50^\circ C$

  3. $100^\circ C$

  4. room temperature

Show answer
Correct Option: D
Explanation:
When it is raining, the dew point is room temperature.
The dew point is the temperature at which air can hold the amount of mixture present in atmosphere. If the temperature falls below it, some water vapour must condense.

When the room temperature becomes equal to the dew point, the relative humidity of the room is

dew point and humidity heat physics

  1. $100$%

  2. Zero%

  3. $70$%

  4. $85$%

Show answer
Correct Option: A
Explanation:

Relative humidity is the ratio of water vapor pressure and saturation vapor pressure at the present temperature.
When the room temperature becomes equal to the dew point, then the air is saturated. Hence the relative humidity of room is $100$ %.

We feel most comfortable at relative humidity at:

dew point and humidity heat physics

  1. < 50%

  2. 50%

  3. > 50%

  4. 100%

Show answer
Correct Option: B
Explanation:

Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity which depends on the air temperature. A reading of 100 percent relative humidity means that the air is totally saturated with water vapour and cannot hold any more, creating the possibility of rain. We feel most comfortable at relative humidity 50%.

On a day during the Monsoon season, the relative humidity at a place is 90% and the temperature is $15^\circ$ (C) The saturation vapour pressure of water at this temperature is $0.0169\, \times\, 10^5$ Pa. The partial pressure of water vapour in the air on that day is

dew point and humidity heat physics

  1. $0.9\, \times\, 10^5$ Pa

  2. $0.0169\, \times\, 10^5$ Pa

  3. $0.0152\, \times\, 10^5$ Pa

  4. $1.0\, \times\, 10$^5$ Pa

Show answer
Correct Option: C
Explanation:
Relative humidity=$\dfrac { \text{Partial pressure of }{ H } _{ 2 }0 }{ \text{Vapour pressure of } { H } _{ 2 }0 }\times100\%$
Let the partial pressure of $H _20$ be $x\rho a$
$90=\dfrac { x }{ 0.169\times { 10 }^{ 5 } } \times 100\\ $
$\dfrac { 90 }{ 100 } \times \dfrac { 169 }{ { 10 }^{ 4 } } \times { 10 }^{ 5 }=x$
$x=169\times9$
$x=1521\rho a$
$=0.0152\times10^5\rho a$

When air is saturated, it cannot hold ____________.

dew point and humidity heat physics

  1. more water vapour

  2. more air

  3. more carbon dioxide

  4. more oxygen

Show answer
Correct Option: A
Explanation:

When a volume of air at a given temperature holds the maximum amount of water vapour, the air is said to be saturated.

At dew point. RH is _______.

dew point and humidity heat physics

  1. 10%

  2. 30%

  3. 50%

  4. 100%

Show answer
Correct Option: D
Explanation:
The dew point is the temperature at which air is saturated with water vapor, which is the gaseous state of water. The relative humidity is 100 percent when the dew point and the temperature are the same.

The relative humidity on a day when partial pressure of water vapour is $0.012 \times 10^5 Pa$ at $12^oC$ is (Take vapour pressure of water at this temperature as $0.016 \times 10^5$ Pa)

dew point and humidity heat physics

  1. 70%

  2. 40%

  3. 75%

  4. 25%

Show answer
Correct Option: C
Explanation:

Given,

Partial pressure of water vapour $={ 0.125\times 10 }^{ 5 }$ Pa
Vapour pressure of water$={ 0.016\times 10 }^{ 5 }$ Pa
Relative humidity at a given temperature (R) 
$=\dfrac { Partial\quad pressure\quad of\quad water\quad vapour }{ vapour\quad pressure\quad of\quad water } \ =\dfrac { { 0.125\times 10 }^{ 5 } }{ { 0.016\times 10 }^{ 5 } } \ =0.75\ =75%$

Formation of dew is an example for ......

dew point and humidity heat physics

  1. Boiling

  2. Melting

  3. Condensation

  4. Evaporation

Show answer
Correct Option: C
Explanation:

It is a example of condensation.Condensation is the process in which gas changes into a liquid when it touches a cooler surface.


Dew drops are formed due to condensation of water vapors. Air around us contains water vapors which we call moisture or humidity. Hot air contains more moisture as compared to cold air. During the night when the hot air comes into contact with some cold surface, water vapor present in it condenses on the cold surface in the form of droplets. These tiny drops of water are called dew drops

When it is raining, the dew point is:

dew point and humidity heat physics

  1. 0$^o$C

  2. 60$^o$C

  3. 100$^o$C

  4. room temperature

Show answer
Correct Option: D
Explanation:
The dew point is the temperature at which the air can exactly hold the amount of moisture present. When raining, at any given temperature, the atmosphere can hold so much water vapour. So the dew point is equal to the room temperature.
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