Chapter 3 - Humidity and Clouds
Q 1. Match the column and complete the chain:
| A | B | C |
|---|---|---|
(A) Cirrus | (i) Vertical extent in the sky | (a) Roaring clouds |
(B) Cumulonimbus | (ii) higher altitude | (b) Floating clouds |
(C) Nimbostratus | (iii) Medium altitude | (c) continuous rainfall |
(D) Alto-cumulus | (iv) Low altitude | (d) snowflake clouds |
Ans:
| A | B | C |
|---|---|---|
(A) Cirrus | (ii) higher altitude | (b) Floating clouds |
(B) Cumulonimbus | (i) Vertical extent in the sky | (a) Roaring clouds |
(C) Nimbostratus | (iv) Low altitude | (c) continuous rainfall |
(D) Alto-cumulus | (iii) Medium altitude | (d) snowflake clouds |
Q 2. Choose the correct word from the brackets and complete the sentence:
(Cumulonimbus, Relative humidity, Absolute humidity, Condensation, Vapour-holding capacity)
(a) The ______ of air is dependent on the temperature of air.
Ans: vapour holding capacity
(b) The amount of vapour in 1 cu.m. of air shows the ______.
Ans: absolute humidity
(c) As ______ is less in desert areas, the air is dry there.
Ans: relative humidity
(d) ______ type of clouds are indicators of storms.
Ans: Cumulonimbus
(e) In a free environment, the ______ of the vapour present in the atmosphere takes place around dust particles.
Ans: condensation
Q 3. Differentiate between:
(a) Humidity and clouds
Ans:
| Humidity | Clouds |
|---|---|
(i) Humidity refers to the quantity of water vapour present in the atmosphere. | (i) Clouds refer to a collection of water vapour at a greater height in the sky. |
(ii) Humidity determines whether the air is dry or damp. | (ii) Clouds depend on the process of condensation for their formation. |
(iii) Humidity can be classified into two types: Absolute Humidity and Relative Humidity. | (iii) Clouds are divided into different types: High clouds, Medium clouds, Low clouds and Cumulonimbus clouds. |
(b) Relative humidity and Absolute humidity
Ans:
| Relative Humidity | Absolute Humidity |
|---|---|
(i) It is expressed as a percentage of the amount of water vapour present in the air to the vapour holding capacity of the atmosphere at the same temperature and same volume. | (i) It is the measure of water vapour in 1 cu.m. of air. |
(ii) It is affected by geographic location and temperature of a particular region. | (ii) It is influenced by the land and water distribution on earth as well as seasonal changes. |
(iii) Relative humidity is expressed in a percentage. | (iii) Absolute Humidity is expressed in grams or kilograms per cubic metre. |
(iv) It is subject to change with a change in the amount of water vapour. | (iv) It remains relatively constant. It contains an absolute measure of moisture in the atmosphere. |
(c) Cumulus clouds and cumulonimbus clouds
Ans:
| Cumulus clouds | Cumulonimbus clouds |
|---|---|
(i) Cumulus clouds are formed due to the vertical flow of air. | (i) When the vertical flow of the air increases, the cumulus clouds gradually transform into Cumulonimbus clouds. |
(ii) Cumulus clouds appear huge and are dome-shaped. | (ii) Cumulonimbus clouds appear like huge mountains and have an anvil shaped top portion. |
(iii) These clouds are grey in colour❘ and are responsible for fair and pleasant weather. | (iii) These are dark coloured clouds which cause thunder and lightning. |
(iv) These clouds are also called ‘fair weather clouds. | (iv) These clouds are also known as ‘thunderheads’. |
Q 4. Answer the following questions:
(a) Why is the air in a region dry?
Ans: Due to the low amount of the moisture in the air, the air in a region is dry.
(b) How is humidity measured?
Ans:
(i) The amount of water vapour in 1 cu.m. of air is called the absolute humidity.
(ii) Absolute humidity is measured with the help of the following formula:
Absolute humidity = \(\large \text \frac {Mass of water vapour}{Volume of air}\)
(iii) The amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature is called relative humidity.
(iv) Relative humidity is measured with the help of the following formula:
Relative humidity (%) = \(\large \text \frac {Absolute humidity}{Vapour-holding capacity}\) × 100
(c) What are the prerequisites for condensation?
Ans: High relative humidity and dew point temperature of the air are the prerequisites for condensation.
(d) What is a cloud? Write its types.
Ans: A visible mass of fine particles of ice and water accumulated around the dust particles in the air at high altitude is called a cloud.
The types of clouds are:
(i) High clouds: Clouds at an altitude of 7000 m to 14000 m are considered as high clouds. Cirrus, Cirro-Stratus and Cirro Cumulus are high clouds.
(ii) Medium clouds: Clouds at an altitude of 2000 m to 7000 m are considered as medium clouds. Alto-Stratus and Alto Cumulus are medium clouds.
(iii) Low clouds: Clouds at an altitude of less than 2000m are considered as low clouds. Strato Cumulus, Stratus, Nimbostratus, Cumulus and Cumulonimbus are low clouds.
(e) Which type of clouds give rain?
Ans: Nimbostratus and cumulonimbus type of clouds give rain.
(f) On what does the percentage of relative humidity depend?
Ans: The percentage of relative humidity depends on the absolute humidity and vapour-holding capacity of the air at a given temperature.
Q 5. Give geographical reasons:
(a) Clouds float in the sky.
Ans:
(i) The condensed water or fine particles of snow accumulate around dust particles at high altitude, leading to the formation of clouds.
(ii) The condensed water or fine particles in the clouds are almost weightless.
(iii) Therefore, clouds float in the sky.
(b) The proportion of relative humidity changes according to altitude.
Ans:
(i) The temperature is found to be comparatively high in areas at sea level. Due to the high temperature, the moisture-holding capacity of air near sea level is found to be high. Therefore, the humidity of the air at sea level is comparatively high.
(ii) The temperature is found to be comparatively low in areas at high altitude. Due to low temperatures, the moisture-holding capacity of air at high altitudes is found to be low. Therefore, the humidity of the air at high altitudes is comparatively low.
(iii) In this way, the proportion of relative humidity changes according to the altitude.
(c) Air becomes saturated.
Ans:
(i) At a certain temperature, the moisture-holding capacity of air gets fulfilled, and it becomes equal to the proportion of moisture present in it.
(ii) At this state, no more moisture can be absorbed by the air.
(iii) Thus, the air becomes saturated.
(d) Cumulus clouds change into cumulonimbus clouds.
Ans:
(i) Cumulus clouds are found between 500 m and 6000 m altitude. They are mostly formed due to the vertical flow of air.
(ii) Sometimes, the vertical expanse of the cumulus clouds increases, which leads to the formation of huge mountain-like cumulonimbus clouds.
(iii) Thus, cumulus clouds change into cumulonimbus clouds.
Q 6. Solve the following:
(a) When the temperature of the air is 30° C, its vapour-holding capacity is 30.37 gms / cu.m. If absolute humidity is 18 gms / cu.m. then what would be the relative humidity?
Solution:
Relative humidity is measured with the help of the following formula:
Relative humidity (%) = \(\large \text \frac {Absolute humidity}{Vapour-holding capacity}\)
∴ Relative humidity (%) = \(\large \text \frac {18}{30.37}\) × 100
∴ Relative humidity (%) = 59.26 %
Ans: The relative humidity is 59.26 %.
(b) What would be the absolute humidity of air if 1 cu.m. air contains 4.08 gms of vapour at 0°C temperature?
Solution:
Absolute humidity is measured with the help of the following formula:
Absolute humidity = \(\large \text \frac {Mass of water vapour}{Volume of air}\)
∴ Absolute humidity = \(\large \text \frac {4.08}{1}\)
∴ Absolute humidity = 4.08 g/cm³
Ans: The absolute humidity is 4.08 g/cm³.
Q 7. Collect the weather related information from newspapers for the month of July. Relate the difference in the maximum and minimum temperatures with humidity.
Ans: Students must do this on their own.