Name the heat that is lost during evaporation and passes into water vapour in a hidden form and is released in the atmosphere during condensation.
- Condensed heat
- Humidity
- Latent heat
- Relative Humidity
Answer
Latent heat
Reason — Latent heat is the heat absorbed during evaporation and stored in water vapour without causing a rise in temperature. It is released into the atmosphere during condensation, warming the surrounding air.
Which, amongst the following, is NOT one of the factors favouring evaporation?
- Humidity
- Supply of heat
- Winds
- Precipitation
Answer
Precipitation
Reason — Precipitation is not a factor favouring evaporation. The factors favouring evaporation are humidity, supply of heat and winds. Precipitation is instead the process by which the products of condensation fall to the ground.
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:
- Humidity
- Dew Point
- Relative humidity
- Latent heat
Answer
Relative humidity
Reason — Relative humidity is 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. It is generally expressed as a percentage and is the essential characteristic of weather forecasts.
The temperature at which air gets fully saturated:
- Humidity
- Dew Point
- Relative humidity
- Latent heat
Answer
Dew Point
Reason — Dew point is the temperature at which air gets fully saturated. Saturated air will not hold any more water vapour at that temperature and its relative humidity becomes 100%.
Assertion (A): Under conditions of high relative humidity, the rate of evaporation of sweat from the skin decreases and the human being feels warm and uncomfortable.
Reason (R): The human body dissipates heat through perspiration and its evaporation.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R does not explain A.
- A is true but R is false.
- A is false but R is true.
Answer
Both A and R are true and R is the correct explanation of A.
Explanation — The human body cools itself through perspiration and the evaporation of sweat. When the relative humidity is high, the air already contains a large amount of water vapour, so evaporation of sweat slows down. As a result, the body loses heat less efficiently, making a person feel warm and uncomfortable.
The measure of the actual amount of water vapour in the air, regardless of temperature:
- Absolute Humidity
- Humidity
- Dew Point
- Relative Humidity
Answer
Absolute Humidity
Reason — Absolute humidity is the amount of water vapour held by air at a certain temperature and volume, regardless of temperature. It is expressed as grams of moisture per cubic metre of air (g/m3).
The process by which products of condensation, viz. water droplets, ice crystals, sleet etc. fall to the ground:
- Evaporation
- Humidation
- Precipitation
- Condensation
Answer
Precipitation
Reason — Precipitation is the process by which the products of condensation, viz. water droplets, ice crystals, sleet, etc., fall to the ground. Rainfall, snowfall, drizzle, sleet and hail are its chief forms.
Which of the following type of cloud has a cauliflower-like shape?
- Cirrus
- Cumulus
- Strata
- None of the above
Answer
Cumulus
Reason — Cumulus clouds have a cauliflower-like appearance with a flat base and rounded, dome-shaped tops. They usually indicate fair weather, though when they grow into cumulonimbus clouds, they bring heavy rain and thunderstorms. Cirrus clouds are thin and feathery, while stratus clouds form uniform layers.
Condensation nuclei are
- impurities that support condensation.
- water particles that help in precipitation.
- droplets formed as a result of condensation.
- droplets that fall to the ground.
Answer
impurities that support condensation
Reason — Condensation nuclei are the impurities present in air, such as minuscule particles of dust, salt and smoke, around which water vapour condenses. Without condensation nuclei, condensation does not take place.
Which of the following is incorrect
- Frontal rainfall: cyclones
- Convectional rainfall: 4 o'clock showers
- Cyclonic rainfall: mountains
- Relief rainfall : mountain barriers
Answer
Cyclonic rainfall: mountains
Reason — Cyclonic or frontal rainfall is caused by the convergence of two air masses with different temperatures, irrespective of relief or convection. Hence, it is not associated with mountains. It is relief or orographic rainfall that is caused by mountain barriers.
In the month of August after many rainy days there was a clear Sunday. We went for a picnic to a park. We felt so hot and uncomfortable that we changed plans and went to watch a movie instead. What caused us this discomfort?
- Latent heat released as a result of condensation raised the temperature.
- High humidity due to the rains of the previous day.
- Heat released from the surface of the earth raised the temperature.
- None of the above.
Answer
High humidity due to the rains of the previous day.
Reason — After several rainy days, the air contains a high amount of water vapour (high relative humidity). Under such conditions, sweat evaporates slowly, reducing the body's ability to lose heat through perspiration. As a result, the air feels hot, sticky, and uncomfortable.
Jyoti and her family had gone to the Little Andaman Island for a holiday. It was a clear day when the sky became dark with clouds and there was heavy rain late in the afternoon. This was the case every day that they spent there. What type of rainfall is this?
- Relief
- Convectional
- Cyclonic
- Frontal
Answer
Convectional
Reason — Little Andaman Island, being close to the Equator, experiences intense heating during the day. The warm, moist air rises by convection, cools, condenses into clouds, and produces heavy afternoon rainfall. This type of rainfall, which commonly occurs around 4 p.m. in equatorial regions, is known as convectional rainfall or the "4 O'clock Shower."
What determines the amount of water vapour in the air?
Answer
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.
How is relative humidity determined?
Answer
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.
Name four chief forms of condensation.
Answer
Four chief forms of condensation are-
- Clouds
- Dew
- Frost
- Fog and mist
Mention the different forms of precipitation.
Answer
The different forms of precipitation are-
- Rain
- Snow
- Hail
Give one difference between fog and mist.
Answer
| Fog | Mist |
|---|---|
| Droplets of water suspended in the atmosphere close to the surface of the earth are termed as fog. | It refers to the formation of clouds due to change in temperature or change in humidity. |
What do you understand by 'condensation nuclei'?
Answer
Condensation occurs only around tiny solid particles like dust or carbon dioxide in smoke. These impurities in air are known as condensation nuclei.
State the three types of rainfall.
Answer
The three types of rainfall are-
- Convectional rainfall
- Orographic rainfall
- Cyclonic rainfall
Why is orographic rainfall also called relief rainfall?
Answer
Orographic rainfall is also called relief rainfall because it is caused by the relief (mountain barriers) of the land. When moist air is forced to rise over mountains, it cools, condenses, and produces rainfall on the windward side.
What is cyclonic rainfall? What are fronts?
Answer
Cyclonic rainfall is the rainfall caused by the meeting (convergence) of warm and cold air masses in cyclones or depressions, irrespective of relief or convection. Since warm air is lighter, it rises over the cold air, cools, condenses, and produces rainfall.
The boundary between two air masses of different temperatures and other physical properties is called a front. The uplift of warm air along this boundary is known as frontal lifting, which results in cyclonic rainfall.
Precipitation
Answer
The process by which the droplets fall to ground in liquid, solid or frozen form is known as precipitation.
Evaporation
Answer
The process by which water vapour enters the atmosphere on heating is known as evaporation.
Condensation
Answer
The process by which water vapour forms water droplets on cooling is known as condensation.
Humidity
Answer
The amount of water vapour present in air is known as humidity.
What is 'humidity'? How is humidity measured?
Answer
The amount of water vapour present in air is known as humidity.
Humidity of the atmosphere is measured with the help of a hygrometer.
Distinguish between Absolute Humidity and Relative Humidity.
Answer
| Absolute Humidity | Relative Humidity |
|---|---|
| It is the measure of the actual amount of water vapour in the air, regardless of temperature. | It measures water vapour in air but relative to maximum vapour that the air can hold at that temperature. |
| It is expressed as grams of moisture per cubic meter of air. | It 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. |
| The higher the amount of water vapour, the higher is the absolute humidity. | Warm air possesses more water vapour than cold air, so with the same amount of absolute humidity, air will have a different relative humidity depending on temperature. |
| In weather calculations, absolute humidity is generally not taken into account. | It is the essential characteristic of weather forecasts, which indicates the likelihood of precipitation, dew or fog. |
Give a geographical reason for each of the following:
(i) The total volume of water in the oceans and seas remains constant.
(ii) In Equatorial regions the sky often remains overcast with clouds.
(iii) When relative humidity is 100% the temperature reading on both wet and dry thermometers is the same.
Answer
(i) The total volume of water in the oceans and seas remains almost constant because the water lost through evaporation is returned by precipitation directly into the oceans and indirectly through rivers and surface run-off. This continuous water cycle maintains the overall balance.
(ii) In the Equatorial region, intense heating causes warm, moist air to rise by convection. As it rises, it cools and condenses to form cumulonimbus clouds, keeping the sky overcast and producing frequent afternoon rainfall.
(iii) When the relative humidity is 100%, the air is fully saturated with water vapour. Since no evaporation takes place from the wet bulb, there is no cooling, and both the wet-bulb and dry-bulb thermometers record the same temperature.
Draw a well labelled diagram showing orographic rainfall.
Answer
Below labelled diagram shows orographic rainfall:
What is condensation? Explain briefly the process of condensation.
Answer
Condensation is the process by which water vapour changes into tiny water droplets on cooling.
Condensation occurs when moist air cools to its dew point or when additional water vapour is added to saturated air. During this process, the latent heat stored in water vapour is released into the atmosphere, and the water vapour condenses around dust or salt particles (condensation nuclei) to form tiny water droplets, leading to the formation of clouds, fog, dew, or rain.
Explain the atmospheric conditions that favour condensation.
Answer
The atmospheric conditions that favour condensation are-
- There should be a high amount of water vapour present in atmosphere.
- Minuscule particles of dust, salt and even smoke act as condensation nuclei.
- The temperature of air must be below dew point temperature so as to encourage condensation.
Give a geographical reason for each of the following:
(i) Condensation is the reverse process of evaporation.
(ii) Coasts receive more rainfall than the interior of the continents.
(iii) The windward sides of mountains receive more rainfall than the leeward sides.
Answer
(i) Condensation is the reverse process of evaporation because evaporation changes liquid water into water vapour by heating, whereas condensation changes water vapour back into liquid water by cooling.
(ii) Coastal areas receive more rainfall because moist winds from the sea contain abundant water vapour. As these winds move inland, they gradually lose their moisture through rainfall, so the interior regions receive less rainfall.
(iii) The windward side receives more rainfall because moist air is forced to rise over the mountain, where it cools, condenses, and produces rainfall. On the leeward side, the air descends, becomes warmer and drier, reducing relative humidity and resulting in little or no rainfall (rain shadow region).
Draw a well labelled diagram showing convectional rainfall.
Answer
Below labelled diagram shows convectional rainfall:
How is dew formed? What is the difference between fog and mist?
Answer
When water vapour condenses on the surface, it forms tiny droplets of water called dew.
The difference between fog and mist is as follows-
| Fog | Mist |
|---|---|
| Droplets of water suspended in the atmosphere close to the surface of the earth are termed as fog. | It refers to the formation of clouds due to change in temperature or change in humidity. |
| The density of fog is quite high. | The density of mist is quite low. |
| The visibility in fog is lower when compared to mist. | The visibility in mist is higher when compared to fog. |
| The duration of fog is comparatively longer than mist. | The duration of mists is comparatively shorter than fog. |
Describe briefly the orographic and convectional rainfall.
Answer
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.
Give a geographical reason for each of the following:
(i) A rain shadow area is generally dry.
(ii) Frontal rain is common in mid-latitudes.
(iii) Convectional rainfall is called 4 o'clock rainfall.
Answer
(i) The windward side of a mountain receives rainfall because moist air is forced to rise, cool, condense, and produce precipitation. As the air descends the leeward side, it becomes warmer and drier due to compression, reducing its relative humidity. Therefore, there is little or no rainfall on the leeward side, forming a rain shadow area.
(ii) Frontal rainfall is common in the mid-latitudes because warm tropical air masses meet cold polar air masses. The lighter warm air rises over the cold air along a front, cools, condenses, and produces rainfall.
(iii) Convectional rainfall is called "4 O'clock Rainfall" because intense heating during the day causes warm, moist air to rise by convection. The air cools, condenses, and produces heavy rainfall, which typically occurs in the late afternoon (around 4 p.m.), especially in equatorial regions.
Define precipitation. Explain briefly the three forms of precipitation.
Answer
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-
Rain — It is the most common form of precipitation. Raindrops of smaller size and less intensity are known as drizzle.
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.
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.
Condensation is regarded as the reverse process of evaporation. Imagine if this reverse process does not happen, what would be its consequences on climate and human beings? Also state the conditions under which this reversal may not happen.
Answer
If condensation did not occur, it would have serious consequences for both climate and human beings.
Climate consequences —
- No cloud formation — Without condensation, clouds would not form.
- No or very little rainfall — The absence of condensation would disrupt precipitation, leading to droughts.
- Disrupted water cycle — Water vapour would not return to the Earth's surface, disturbing the natural water cycle.
- Hotter climate — The atmosphere would retain more water vapour, leading to changes in weather and climate.
Human consequences —
- Acute water scarcity for drinking, irrigation, and industries.
- Crop failure and food shortages due to lack of rainfall.
- Damage to ecosystems and loss of biodiversity because plants and animals depend on rainfall for survival.
Conditions under which condensation may not occur
- The air is not cooled to its dew point (saturation point).
- The air has very low humidity (insufficient water vapour).
- There are no condensation nuclei (such as dust, smoke, or salt particles) for water vapour to condense upon.
Name two physical objects in your home which are affected by humidity. Also state the reason for such an affect.
Answer
Two physical objects in my home which are affected by humidity are:
- Wooden furniture — High humidity causes the wood to absorb moisture and swell, while low humidity may cause it to shrink and crack
- Electronic devices (TV, computer, or smartphone) — High humidity causes moisture to accumulate inside the devices, which can corrode electrical components and affect their functioning.
List two places which receive two types of rainfall. Give reasons to support your answer.
Answer
Two places which receive two types of rainfall are:
Western Ghats receive both orographic rainfall and convectional rainfall.
- Moist winds from the Arabian Sea rise over the mountains, causing heavy orographic rainfall on the windward side.
- 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.
- Moisture-laden winds from the Bay of Bengal encounter the Eastern Himalayas, resulting in significant orographic rainfall on the windward side.
- Warm and humid conditions contribute to convective cloud formation, leading to heavy convectional showers and thunderstorms.
List the forms of precipitation that occur in your city along with the time of year when they occur.
Answer
The forms of precipitation that occur in my city are:
- Rain — Rainfall is most common during the monsoon season, which extends from June to September. The heaviest rainfall occurs in July and August.
- 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.
- Fog, Mist and Dew — In winters, mornings are foggy in my city and there is a lot of dew at night.