ICSE-IX-Geography
13: Insolation
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- #Section : VIPractice Questions
- Qstn #1State the importance of insolation.Ans : Importance of insolation:
- The radiant energy received by the earth from the sun is called the incoming solar radiation or insolation.
- The insolation received by the earth is responsible for all forms of activity on the Earth.
- The circulation in the atmosphere is due to the differential heating of the atmosphere by insolation.
- The radiant energy from the sun enables plants to manufacture their own food. This forms the basis for food needed by all other organisms on the Earth.
- The circulation of ocean water is also due to the unequal heating of the ocean water by insolation.
- Qstn #2Why does only 51% of the insolation reach the Earth’s surface ?Ans : Only 51% of the insolation reaches the earth’s surface because 35% is reflected back into space by the atmospheric layers and 14% is absorbed by the atmosphere.
- Qstn #3What do you understand by daily range of temperature and annual range of temperature ?Ans : The difference between the maximum and minimum temperature recorded in a particular day at a place is called daily range of temperature. It is low in coastal areas while it is high in deserts and in interiors of continents.
The difference between the mean temperature of the hottest month (July) and mean temperature of the coldest month is called the annual range of temperature. It is low equatorial region, while it is high in polar areas.
- Qstn #4Define the following :
(a) Daily Mean Temperature.
(b) Monthly Mean Temperature.
(c) Annual Mean Temperature.
(d) Mean Temperature of a place.Ans : (a) Daily Mean Temperature — The average of the maximum temperature and minimum temperature recorded during a day (24 hours) is known as daily mean temperature.
Daily Mean Temperature
= (Max Temp. + Min. Temp.)/2
= (39° + 27°)/2
= 66°/2
= 33°C
For example, if a place has the maximum temperature of 39°C and minimum temperature of 27°C for a particular day, the daily mean temperature.
(b) Monthly Mean Temperature — The average of the daily mean temperature of all days of a month is known as monthly mean temperature.
Monthly mean temperature of July
= (Daily mean temperature 1 + 2 + 3 ...... 31 days)/31
(c) Annual Mean Temperature — The average of daily mean temperature of all days of a year is known as Annual mean temperature.
Annual mean temperature of year 2010
= (Daily mean temperature of 1 + 2 + 3 ......365)/365
(d) temperature of a place is obtained by collecting the data for a period of 30 - 40 years. The average of mean annual temperature of a place is calculated. This is also known as normal temperature of a place.
Mean temperature
= (Mean annual temp. of 1986 + 1985 ......... for 35 years)/35
Mental climate.
- Qstn #5Distinguish between maritime climate and continental climate.Ans : The nearness to sea has a moderating influence on the temperature of coastal areas. Maritime or equable temperatures are found in coastal areas. But extremes of temperatures, with a continental climate, are found in inland areas remote from the sea. Due to the presence of land breezes and sea breezes in coastal areas : the summers are warm and winters are cool. This is due to the differential heating and cooling of land and water. Land surfaces are heated more quickly than water. But a greater annual range of temperature is found as we go away from the equator. The climate of Mumbai is more equable than that of Delhi.
- Qstn #6Explain the importance of insolation.Ans : Sun is the most important source of atmospheric heat. Sun’s diameter is more than 100 times the Earth’s diameter and has a surface temperature of more than 10,000 °F. The heat waves radiate from the sun in all directions at a speed 186,000 miles per second of 3 lakh km per second. The solar radiation received by the earth is 1/2000 millionth part of solar output. Yet, this small amount is vital for our existence on the earth. It is estimated that, on the average the earth receives about 1.9 g calories per minute per sq. cm. This is known as ‘solar constant’. All the physical phenomena depend upon insolation. Winds and ocean currents originate due to insolation. The earth is habitable only due to insolation.
- Qstn #7Explain the Greenhouse effect of atmosphere.Ans : Atmosphere is heated by the radiation from the earth’s surface below. This action is compared to that of a glasshouse of greenhouse in which vegetable and flowers are grown in polar areas. Glasshouse permits radiation to get in but does not allow radiation to escape out. Therefore, glasshouse is warmer from inside than outside. Atmosphere also acts like a blanket keeping the earth warm. It is known as greenhouse effect of atmosphere. This is due to presence of carbon dioxide in atmosphere. Carbon dioxide has the ability to absorb earth radiation. The carbon dioxide layer acts as a glass roof of the greenhouse. With the increase in carbon dioxide, the temperature of the earth is increasing. Due to this, the year 1955 was the hottest year in India during this century.
- Qstn #8What is global warming ? What are its causes ? State its effects.Ans : Global warming : The burning of fossil fuels, (coal, gas, petroleum), the cultivation of soil, large scale industrialisation, rapid means of transport and deforestation has caused an imbalance in the atmosphere. These activities are increasing the amount of carbon dioxide. Thus, greenhouse effect has raised the average, temperature of the earth by 0.5°C. By the year 2000, the earth’s, average temperature will go up by 2°C. This is called global warming. Global warming is causing a rise in sea-levels due to melting of glaciers. It is threatening to submerge many coastal areas.
- Qstn #9Mountains are cooler than plains. Discuss.Ans : The temperature decreases with height at the rate of 1°C per 165 metres or about 0°C per kilometre. The atmosphere is heated by radiation from the earth below. Therefore, lower layers are warmer than higher layers. There is absence of water vapour and dust
particles on high mountains. So there is unchecked radiation. That is why mountains are cooler than plains. Shimla is cooler than Delhi. Similarly, Nainital is cooler than Allahabad.
- Qstn #10“Winter nights at Delhi are cooler than in Mumbai”. Why?Ans : Mumbai has an equable climate due to coastal location, while Delhi is an inland town. The presence of land and sea breezes keep the nights warm at Mumbai.
- Qstn #11Vertical rays are Hotter than slanting rays. Why ?Ans : Vertical rays are hotter than slanting rays due to the following reasons:
- Vertical rays heat up a smaller surface. Hence, the heat received per unit of area is large. On the other hand, slanting rays heat up a large area.
- Vertical rays travel through a shorter distance in the atmosphere and the loss of heat is less. Slanting rays travel a longer distance through the atmosphere where much of its heat is absorbed by clouds, water vapour and dust particles.
- Qstn #12Why is noon hotter than morning and evening ?
Or
Maximum temperatures are found in the afternoon. Why?Ans : The sun is overhead at noon. The Sun rays are almost vertical. But in the morning and evening, the angle of Sun rays is oblique. Slanting rays fall in the morning and evening. Vertical rays are hotter than slanting rays. As the vertical rays give more heat per unit area, the noon is hotter than morning and evening.
- Qstn #13‘Despite its location in higher latitudes, the coast of Norway is never frozen.’ Why ?Ans : The areas situated in higher latitudes have a cold climate. In winter, these areas have temperatures below freezing point (0°C). But coast of Norway is never frozen. Its ports are ice free. North Atlantic Drift (Gulf Stream currents) flows along its coast. It is a warm current which raises the winter temperatures of this area.
- Qstn #14Why are the northern slopes of Himalayas cooler than its southern slopes ?Ans : The Northern Slopes of Himalayas are away from the Sun. These slopes get oblique rays. These slopes are exposed to cold winds. These are shady slopes and are cooler. But the Southern Slopes are Sun facing slopes. These get Sun’s rays more directly and also for longer periods. These are Sunny slopes and shelters from cold winds. So the Southern Slopes of Himalayas are warmer than northern slopes.