Humidity

Latent heat

Precipitation

Relative humidity

Dew Point

Both A and R are true and R is the correct explanation of A.

Explanation — Human comfort depends on humidity. Highly humid air is more oppressive. The human body dissipates heat through perspiration and its evaporation. Under conditions of high relative humidity, the rate of evaporation of sweat from the skin decreases which results in the human being feeling warm and uncomfortable.

Absolute Humidity

Precipitation

Cumulus

impurities that support condensation

Cyclonic rainfall: mountains

High humidity due to the rains of the previous day.

Convectional

The process by which the droplets fall to ground in liquid, solid or frozen form is known as precipitation.

The process by which water vapour enters the atmosphere on heating is known as evaporation.

The process by which water vapour forms water droplets on cooling is known as condensation.

The amount of water vapour present in air is known as humidity.

The forms of precipitation that occur in my city are:

1. Rain — Rainfall is most common during the monsoon season, which extends from June to September. The heaviest rainfall occurs in July and August.
2. Hail — Hailstorms are relatively rare in my city, but they can occur during the pre-monsoon months of March to May. These storms are more sporadic and less frequent compared to rainfall.
3. Fog, Mist and Dew — In winters, mornings are foggy in my city and there is a lot of dew at night.

The amount of water vapour in the air is determined by temperature. The hotter the air, the more the water vapour present in it. When the atmospheric temperature is low, water vapour is less.

Relative humidity is expressed as the ratio between the absolute humidity of a given mass of air and the maximum amount of water vapour that it can hold at the same temperature.

Four chief forms of condensation are-

1. Clouds
2. Dew
3. Frost
4. Fog and mist

The different forms of precipitation are-

1. Rain
2. Snow
3. Hail

Condensation occurs only around tiny solid particles like dust or carbon dioxide in smoke. These impurities in air are known as condensation nuclei.

The three types of rainfall are-

1. Convectional rainfall
2. Orographic rainfall
3. Cyclonic rainfall

Orographic rainfall is caused by the relief of the land as it occurs from the cooling of warm moist air which ascends above the mountain barrier lying in the direction of the prevailing winds. The presence of mountains causes humid air to rise. The sudden ascent causes cooling of air, leading to condensation and precipitation. Hence, it is also called relief rainfall.

Cyclonic rainfall occurs due to cyclones and depressions irrespective of relief or convection. It is caused by convergence of two different air masses with different temperatures and other physical properties. When warm and cold air masses confront each other, the warmer air generally climbs above the colder air. The boundary zones of these air masses are called the fronts.

The rising air is cooled while undergoing a frontal lift. This causes precipitation. Such precipitation is called cyclonic rainfall.

The amount of water vapour present in air is known as humidity.

Humidity of the atmosphere is measured with the help of a hygrometer.

(i) The total volume of water in the oceans and seas remains constant because all the water that evaporates from the earth's water bodies is eventually returned to it directly by the process of condensation and precipitation, and indirectly by stream and overflow from land surfaces.

(ii) In Equatorial regions the sky often remains overcast with clouds due to excessive heat. The high temperature leads to the rapid heating of air. Such heated air rises in convectional currents, leading to development of clouds at about 10 km height.

(iii) This is because when relative humidity is 100%, the air is fully saturated with moisture and it will not hold any more vapour at that temperature. Since saturated air will not allow evaporation, the temperature reading on both the dry and wet thermometers will be the same.

Below labelled diagram shows orographic rainfall:

The process by which water vapour forms water droplets on cooling is known as condensation.

During condensation, the latent heat locked in water vapour is released back into the atmosphere. Condensation can take place only when water vapour is added to saturated air or when the temperature falls below the temperature at which air becomes saturated.

The atmospheric conditions that favour condensation are-

1. There should be a high amount of water vapour present in atmosphere.
2. Minuscule particles of dust, salt and even smoke act as condensation nuclei.
3. The temperature of air must be below dew point temperature so as to encourage condensation.

(i) Condensation is the reverse process of evaporation as evaporation is the process by which water vapour enters the atmosphere on heating while condensation is the process by which water vapour is converted back to water droplets on cooling.

(ii) Coasts receive more rainfall than the interior of the continents because the humidity in the clouds is high when they are at the coast. When they reach the interior of the continents, they have already shed water in the form of rain, and so, they do not have much humidity left to cause rainfall.

(iii) The windward sides of mountains receive more rainfall than the leeward sides because the sudden ascent of warm moist air on the windward sides causes cooling of air, leading to condensation and precipitation.
On the contrary, on descending the leeward slope, a decrease in altitude increases both the pressure and the temperature, leading the air to get compressed and warm. Consequently, the relative humidity drops and there is evaporation and little or no precipitation in the rain shadow area.

Below labelled diagram shows convectional rainfall:

When water vapour condenses on the surface, it forms tiny droplets of water called dew.

The difference between fog and mist is as follows-

Orographic rainfall — It occurs from the cooling of warm moist air which ascends above the mountain barrier lying in the direction of the prevailing winds. The presence of mountains causes humid air to rise. The sudden ascent causes cooling of air, leading to condensation and precipitation.

Convectional rainfall — This type of rainfall is common in equatorial regions. The high temperature leads to the rapid heating of air. Such heated air rises in convectional currents, leading to development of clouds at about 10 km height. Ascending currents of hot and humid air causes condensation of the clouds, resulting in heavy rainfall.

(i) The sudden ascent of warm moist air on the windward sides causes cooling of air, leading to condensation and precipitation.
On the contrary, on descending the leeward slope, a decrease in altitude increases both the pressure and the temperature, leading the air to get compressed and warm. Consequently, the relative humidity drops and there is evaporation and little or no precipitation in the rain shadow area. Hence, a rain shadow area is generally dry.

(ii) Frontal rain is common in mid-latitudes due to the meeting of the sub-tropical and polar air masses. It is caused by convergence of two different air masses with different temperatures and other physical properties. When warm and cold air masses confront each other, the warmer air generally climbs above the colder air. The rising air is cooled while undergoing a frontal lift. This causes precipitation. Such precipitation is called cyclonic rainfall.

(iii) Convectional rainfall is called 4 o'clock rainfall as this type of rainfall occurs in the afternoon at about 4 o'clock. This is because the heat from the sun builds up throughout the day, causing the air to rise and form clouds that eventually bring rain in late afternoon around 4 o'clock.

The process by which products of condensation, water droplets, ice crystals, sleet, etc., fall to ground is known as precipitation.

The three forms of precipitation are-

1. Rain — It is the most common form of precipitation. Raindrops of smaller size and less intensity are known as drizzle.

2. Snow — Water droplets which rise higher and freeze on account of drop in temperature is called snow. Snowfall usually occurs in winters in cold climates or on high mountains.

3. Hail — Sometimes, vertical air currents may push water droplets or ice particles higher. They form into solid ice and fall as hail. Hailstones cause great damage to crops.

If condensation does not occur, it would have significant consequences on climate and human beings:

Climate consequences —

1. Reduced cloud formation — Without condensation, clouds would be scarce or non-existent, leading to decreased cloud cover and overall cloud-related phenomena.
2. Decreased precipitation — The absence of condensation would result in limited or no rainfall, leading to drought conditions and water scarcity.
3. Disrupted water cycle — Condensation is a key component of the water cycle. Without condensation, the water cycle would be disrupted, affecting the distribution and availability of water resources.

Human consequences —

1. Water scarcity — The lack of condensation and subsequent reduced precipitation would result in water scarcity, affecting drinking water supplies, agriculture, and various industries dependent on water resources.
2. Impact agriculture and food production — Insufficient rainfall due to the absence of condensation would negatively impact agricultural productivity, leading to crop failures and food shortages.
3. Ecosystem disruption — Condensation plays a vital role in sustaining ecosystems by providing water for plants, animals, and other organisms. Without condensation, ecosystems would suffer from water stress, impacting biodiversity and ecological balance.

Possible conditions under which this reversal may not happen are:

1. Extremely low humidity — If the air has extremely low humidity levels, there may not be enough moisture present for condensation to occur.
2. Lack of condensation nuclei — In the absence of sufficient condensation nuclei, condensation may be hindered.
3. Absence of cooling mechanism — Lack of cooling, such as the ascent of air masses or interaction of warm and cold air, hindering condensation.

Two physical objects in my home which are affected by humidity are:

1. Woodwind Musical Instruments like flutes are made of wood and can be impacted by humidity. High humidity can cause the wood to swell, affecting the instrument's structure, playability, and tone while low humidity can lead to the wood drying out, resulting in cracks, leaks, and changes in sound quality.
2. Electronic devices, such as computers, televisions and smartphones can be affected by humidity. High humidity levels can cause moisture to accumulate inside the devices, potentially leading to corrosion of circuitry and electrical components. Excessive humidity may also interfere with proper functioning and performance, causing malfunctions or even permanent damage.

Two places which receive two types of rainfall are:

Western Ghats receive both orographic rainfall and convectional rainfall.

1. Moist winds from the Arabian Sea rise over the mountains, causing heavy orographic rainfall on the windward side.
2. High temperatures and local conditions lead to localized thunderstorms and convectional rainfall.

Northeastern states of Meghalaya and Assam also receive both orographic rainfall and convectional rainfall.

1. Moisture-laden winds from the Bay of Bengal encounter the Eastern Himalayas, resulting in significant orographic rainfall on the windward side.
2. Warm and humid conditions contribute to convective cloud formation, leading to heavy convectional showers and thunderstorms.