NCERT 7th Class (CBSE) Social Science: Elements of Weather and Climate

Question: How is the atmosphere heated?

Answer: The solar radiations which pass through the atmosphere before reaching the earth’s surface, does not heat the earth’s surface directly. The air resting over the earth’s surface gets heated due. To contact with the hot surface of the earth. This heat is further transmitted to the upper layers and the atmosphere is heated.

Question: What do you mean by humidity in the atmosphere? How do we express it?

Answer: Humidity in the atmosphere:

1. The actual amount of water vapor present in our is called humidity or absolute humidity.
2. It is expressed in two ways-absolute humidity and relative humidity.
3. Relative humidity is defined as the ratio between the actual amount of water vapor present in the air at a given temperature and the maximum capacity of air to hold moisture at that temperature.
4. Relative humidity is always expressed in while absolute humidity determines the amount.

Question: Explain the factors responsible for the changes in atmosphere pressure on the earth’s surface.

Answer: The factors responsible for the changes in atmosphere pressure on the earth’s surface are:

1. Temperature of the air: The hot air being light rise up and creates an area of low pressure whereas cold air being heavy settles down and creates an area of high pressure. Thus atmosphere pressure decreases with increase in temperature and increases with decrease in temperature.
2. Density of air: The density of air column is more at the sea level and less under mountains. Hence atmosphere pressure is more at the sea level and less on the mountains.
3. Highest of the place above the mean sea level: The atmosphere pressure decreases with increase in altitude. Thus atmosphere pressure is highest at the sea level and less on the mountains.
4.  Amount of moisture present in air: The most air exerts less pressure while dry air exerts more pressure.

Question: Describe the main features of planetary winds or prevailing winds.

Answer: Some winds blow constantly in a particular direction throughout the year. These winds are known as prevailing winds or permanent winds or planetary winds. These winds originate due to the presence of permanent high pressure and low pressure belts on the surface of the earth. The main types of planetary winds are the. Trade winds, the westerlies and the polar winds.

Question: How does the amount of moisture in the atmosphere vary from place place to place and from time to time?

Answer: The amount of moisture present in the air varies from place to place and from time to time:

1. The air in the equatorial region has more moisture than other regions of the world.
2. The air has more moisture during the summer season than during the winds season.
3. The amount of moisture decrease with the increase in height above the mean sea level.
4. The amount of moisture is almost zero in the cold air of the polar regions during the winter months.

Question: Name and explain the various types of rainfalls.

Answer: Convectional rainfall:

1. When the most air gets heated, it becomes light and rises up in the atmosphere. The air further expands, cools and condenses to form clouds to bring rainfall.
2. These clouds reduce sudden and heavy rainfall accompanied by thunder and lightning.
3. It is experienced everyday in equatorial region.

Orographic / relief rainfall:

1. It occurs when moisture bearing winds are forced to rise over a hill or mountain and shed its moisture in the forms of rainfall.
2. This is followed by condensation and precipitation.
3. The windward side of the mountain gets more rainfall than the leeward side.

Cyclonic / frontal rainfall:

1. Where warm and cold air have different densities they not mix in this case.
2. The warm air rises due to its light weight while cold air remains near the surface.
3. The boundary between these air masses is called front.
4. Rising warm air condenses which finally bring rainfall. This type of rainfall is common in westerlies area during winter season.