Notes on Hygrometer and Weather Phenomenon | Grade 11 > Physics > Hygrometry | KULLABS.COM

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#### Wet and Dry Bulb Hydrometer

A hygrometer is a device which is used to measure the relative humidity of the air. A wet and dry hygrometer are the simplest of all the hygrometers.

It consists of two mercury thermometers A and B as shown in the figure. Here, thermometer A is dry which is used to measure room temperature while thermometer B is wet which is use to determine the dew point. The bulb of B is wrapped with wet muslin piece which is in contact with water in a beaker. Due to capillary action, water rises up in muslin piece and evaporates. As a result temperature of thethermometer, B falls down. The temperature is noted after every minute. Finally, hygrometer shows constant temperature. The difference in the reading of the dry and wet thermometers is a measure of relative humidity of the air.

Gas and Vapour

A vapour above the critical temperature is gas and a gas below the critical temperature for the substance is a vapour.

A gas cannot liquefy by the application of pressure alone, how large the pressure may be. On the contrary, a vapour can be liquefied under pressure alone. To liquefy a gas, it must be cooled up to or below its critical temperature. Further, both the vapour and gaseous states obey the same gas laws.

#### Weather Phenomenon

When the temperature of the air falls below a dew point, the condensation, the weather exhibits many phenomena like the formation of dews, hail, cloud, rain, fog, mist etc.

Dew

At night, the surface of the earth radiated heat and its temperature falls. In the morning the temperature of the atmosphere becomes less than a dew point, the water vapour condenses in the form of tiny water drops on the leaves or grasses. Those tiny drops are dews.

Hoarfrost

If the temperature of the temperature falls below 0o C, the dew formed on the leaves and grasses condense directly into solid white grains called hoarfrost.

Fog and Mist

When air gets cooled up to some distance from the ground to a temperature below the dew point, water vapours present in the temperature falls below 0oC, the dew point, water vapours present in the temperature condenses on dust particles in the atmosphere and the mist is formed.

Clouds and Rain

When the temperature of the layers of air at high altitude falls below the dew point, the condensation of water vapour takes place on the dust particles present there and the cloud is formed. When a small drop of water in the cloud combine together, bigger water drops are formed and rainfall occurs due to the gravity.

Snow and Hail

When the cloud passes through a very cold region, the water drops freeze and fall in the form of snow and hail. Snowfall is common in all hill stations because of very low temperature in the winter. Hails are caused due to the freezing of raindrops in the atmosphere. Hails are of different sizes whereas snow is quite soft.

Hygrometer is a device which is used to measure the relative humidity of the air. Wet and dry hygrometer is the simplest of all the hygrometers.

A vapour above the critical temperature is gas and a gas below the critical temperature for the substance is a vapour.

If the temperature of the temperature falls below 0C, the dew formed on the leaves and grasses condense directly into solid white grains called hoarfrost.

When the cloud passes through a very cold region, the water drops freeze and fall in the form of snow and hail.

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• ### ______ is a device which is used to measure the relative humidity of the air.

Spygmomanometer

Hydrometer

Hygrometer

Lactometer

• ### ______ is a device which is used to measure the relative humidity of the air.

Spygmomanometer

Lactometer

Hygrometer

Hydrometer

sublimation
ebullition
evaporation

ebullition
evaporation
sublimation
• ### Hygrometer is instrument for measuring ______.

the density of air

the amount of water vapour in the atmosphere

the amount of oxygen in air

the expansion of water vapour under temperature

• ### Higher difference between temperatures of the wet bulb and dry bulb indicates ______.

lower relative humidity

greater relative humidity

higher dew point

• ### A liquid boils at a temperature at which its saturated vapour pressure becomes ______.

none of the answers are correct

half the atmospheric pressure

equal to atmospheric pressure

twice the atmospheric pressure

• ### If the atmospheric temperature and dew point are nearly equal ______.

relative humidity is zero

nothing can be said about relative humidity

relative humidity 50%

relative humidity is nearly 100%

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