Solar Radiation, Heat Balance and Temperature Class 11 Important Extra Questions Geography Chapter 9
Solar Radiation, Heat Balance and Temperature Important Extra Questions Very Short Answer Type
Question 1.
What is insolation?
Answer:
The incoming solar radiation is called insolation.
Question 2.
How much energy radiated by the sun is intercepted by the earth?
Answer:
Only A of the billionth fraction of the energy radiated from the sun is intercepted by the earth.
Question 3.
What is isotherm?
Answer:
Isotherms are imaginary lines joining places having equal temperatures.
Question 4.
Where does the energy radiate from the sun come from?
Answer:
The energy radiated from the sun comes from nuclear reactions in its core.
Question 5.
What is the temperature at the core of the sun?
Answer:
The temperature at the core of sun-is about 15,000,000°C.
Question 6.
What is the radiant energy of sun commonly known as?
Answer:
The radiant energy of the sun is commonly known as short waves or electromagnetic waves.
Question 7.
At what speed the short waves travel?
Answer:
The short waves travel at a speed of light, i.e., about 2,98,000 km. per second.
Question 8.
What is terrestrial radiation?
Answer:
The longwave radiation, i.e., re-emittance of the energy received from the earth’s surface, is terrestrial radiation.
Question 9.
Name the processes which control the heat budget of the earth ., and the atmosphere.
Answer:
They are the processes of absorption, reflection and scattering.
Question 10.
Define heat budget.
Answer:
The gains and losses in heat by incoming and outgoing radiation is known as heat budget.
Question 11.
What is advection?
Answer:
Transfer of heat through the horizontal movement of the air is called advection.
Question 12.
What is meant by temperature gradient?
Answer:
The rate of change of temperature is called the temperature gradient.
Question 13.
Name two months of the year which represent the seasonal extremes of temperature.
Answer:
January and July months represent the seasonal extreme of temperature.
Question 14.
Define Planck’s law.
Answer:
Planck’s law states that hotter a body, the more energy it will ‘ radiate and shorter is the wavelength of that radiation.
Question 15.
What is specific heat?
Answer:
Specific heat is the energy needed to raise the temperature of one grain of a substance by one degree Celsius.
Question 16.
What is insolation?
Answer:
The incoming solar radiation is termed as insolation. It comes in the form of short waves.
Question 17.
What are the methods by which the atmosphere is heated?
Answer:
The atmosphere gets heated in the following ways:
(a) Radiation,
(b) Conduction,
(c) Convection,
(d) Advection.
Question 18.
Why do isotherms bend while crossing the continents and oceans?
Answer:
Due to differential heating and cooling of land and seawater.
Question 19.
How much energy radiated by the sun is intercepted by the earth?
Answer:
1/2000 million part of the total energy radiated by the sun is intercepted by the earth.
Question 20.
Which is the most important process of heating the atmosphere?
Answer:
Terrestrial radiation.
Question 21.
What is the temperature?
Answer:
Warmth or coolness of the air is called its temperature.
Question 22.
What is the extent of the Torrid Zone?
Answer:
23’/2°N to 23’/2°S.
Question 23.
What is the extent of the Frigid Zone?
Answer:
66V20 to poles.
Question 24.
Name the type of climate found in coastal areas.
Answer:
Maritime (moderate).
Question 25.
Why is the temperature of the earth increasing?
Answer:
Due to the increase in carbon dioxide.
Question 26.
What is insolation?
Answer:
The incoming solar radiation is termed as insolation.
Solar Radiation, Heat Balance and Temperature Important Extra Questions Short Answer Type
Question 1.
What is air drainage?
Answer:
The cold air acts almost like water and moves down the slope to pile up deeply in pockets and valley bottoms with warm air above. This is called air drainage. It protects plants from frost damages.
Question 2.
What are the characteristics of isotherms?
Answer:
Main characteristics of isotherms are:
Isotherms run along the latitudes.
Isotherms take sudden bends at the land-water edge because of land-water contact.
They are drawn at equal space which indicates the latitudinal thermal gradient.
Isotherms change their positions.
Question 3.
Discuss the variation in the distribution of insolation over the earth’s surface.
Answer:
The incoming solar radiation is called insolation. Insolation is * greatest at the equator. It decreases polewards. The total amount of insolation received at the equator is roughly about 4 times of that received at the poles. In tropical regions, the amount of insolation is only large but there is also little seasonal variation. It is because all their places between Tropic of Cancer and Capricorn experience overhead sun twice during the course of a year. Insolation is maximum twice in a belt between 23°30’ and 66°30′.
Question 4.
What are the effects of the atmosphere on insolation?
Answer:
The energy from the sun passes through different layers of the atmosphere before it reaches the ground. Atmospheric gases are essentially transparent to visible light, but suspended particles of liquid or solid material can absorb or reflect light. A thick cloud may allow less than 10% of sunlight to reach the earth’s surface. Clouds generally behave like mirrors. They reflect sunlight off in different directions rather than absorbing. Reflected sunlight is permanently lost from the earth. The blue colour of the daytime sky is due to the scattering of sunlight.
Question 5.
Define temperature.
Answer:
The temperature is the measurement of available or sensible heat energy in a system. It is a measure of hotness or coldness of the body. Such property determines whether the heat will flow out or into an object when it comes in contact with other objects.
Question 6.
Explain why the angle of the sun’s rays falls variably on different latitudes.
Answer:
The earth revolves around the sun once in a year in an elliptical path called the ‘plane of ecliptic’. At the same time, the earth rotates on its axis in 24 hours. The earth’s axis is tilted making an angle of 66°30′ from the plane. Due to inclination of the earth’s axis, the angle of the sun’s rays falling on the earth’s surface varies from vertical on the equator to more and more slanting as one moves towards the poles.
Question 7.
Explain how the ocean currents influence the temperature distribution over the earth surface.
Answer:
Ocean currents are large movements of ocean water from places of warm temperature to colder temperature or vice-versa. Their movement affects the temperature of the adjacent areas. The warm currents raise the temperature of adjoining colder landmasses. The climate of north-western Europe is modified to a large extent by ocean currents of the North Atlantic Ocean. The cold currents of the western coast of South Africa or South America lower the temperature of adjacent warmer lands.
Question 8.
What is the role played by prevailing winds in temperature modification?
Answer:
Prevailing winds also affect the temperature conditions of the areas. The moderating effects of oceans are brought to the adjacent lands through winds. On the contrary, off-shore winds take the effects of warm or cold currents away from the land.
Question 9.
What is the difference between direct radiation and diffused radiation?
Answer:
The sun emits short wave radiation to space and the earth’s surface. The solar energy strikes the upper limits of the atmosphere and it gradually reaches the earth’s surface directly or indirectly (scattered) and is absorbed. It is estimated that out of 100 units of incoming solar energy, 22 units travel directly to the earth’s surface. This energy flow is called direct radiation. Some of the scattered rays eventually also find their way down indirectly to the earth’s surface. They are collectively called diffused radiation.
Question 10.
What is global warming? What are its causes?
Answer:
The burning of fossil fuels, the cultivation of the soil, industrialisation of land on a large scale, rapid means of transport and deforestation have caused an imbalance in the atmosphere. These activities are increasing the amount of carbon dioxide. Thus, the 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. It is causing a rise in the sea level due to melting of glaciers. It is threatening to submerge many coastal areas.
Question 11.
Why do different parallels receive different amounts of insolation?
Answer:
Due to the inclination of the earth’s axis, the angle of the sun’s rays falling on the earth’s surface varies from vertical on the equator to more and more slanting as one moves towards the poles. This latitudinal difference in the angle of incidence of sun’s rays leads to different amounts of insolation received at different parallels.

Fig.9.5: Incidence of the sun’s rays on the earth’s surface
Question 12.
How does the angle of the sun’s rays falling on the ground affect the amount of insolation?
Answer:
The amount of insolation reaching the earth’s surface depends largely on the inclination or angle of the sun’s rays. Vertical rays and those nearly 80 in the lower latitudes are more effective in increasing temperature than the oblique rays in the higher latitudes, although the duration of sunshine may be much longer in the latter case. Moreover, the oblique rays spread over a larger area on the earth’s surface whereas the vertical rays are concentrated over a smaller area, the intensity of heat being lighter in the area insolated by vertical rays.
Question 13.
Differentiate between advection and convection.
Answer:
Transfer of heat through the horizontal movement of the air is called advection, whereas the vertical mixing of the air is termed as convection. Convection is caused by the circulatory movement of the air itself and the pull of gravity.
Question 14.
Isotherms do not show the correct temperature of a place. Discuss.
Answer:
Isotherms show the temperature of a place supposing it to be at sea level. The temperature is reduced to sea level to avoid the effect of relief. Thus, isotherms do not show the actual temperature of a place.
Solar Radiation, Heat Balance and Temperature Important Extra Questions Long Answer Type
Question 1.
Discuss the impact of tilting of earth’s axis on insolation in the northern and southern hemisphere.
Answer:
The earth rotates on its axis in 24 hours. The earth’s axis is tilted at an angle of 66°30′ from the plane.

Fig.9.6 : Solstices and equinoxes
When the northern hemisphere is tilted towards the sun, it receives the maximum amount of insolation. On 21 st June, the sun is overhead the Tropic of Cancer and it is the longest day of the year for the northern hemisphere. All this time, the southern hemisphere is away from the sun and 21st June is the shortest day of the year for the southern hemisphere. On 21st March and 23rd September, the sun is over the equator and the length of the day is the same everywhere throughout the world. This position is called the equinox.
On 21st December, the southern hemisphere is in front of the sun and receives the maximum daylight. It is, however, the tropics that receive the maximum insolation.
Question 2.
Discuss the impact of altitude on temperature over the atmosphere.
Answer:
Altitude is the height of a point above mean sea level, measured vertically. The temperature decreases with increasing height and latitude from the earth’s surface. This vertical decrease in temperature takes place at the rate of 0.65° per 100 metres or 165 metres per 1°C. These variations are normal throughout the troposphere and are termed as normal lapse rate. The atmosphere near the surface is denser and contains a large amount of water vapour and dust particles. Being closer to the land surface, it absorbs more terrestrial heat than that of the upper air. Hence, the temperature is higher in the lower part of the atmosphere than in the upper part, where the air is cleaner. That is why the higher we go, the cooler it is. Ootacamund, Mount Abu, Panchmarhi are cooler in summer than plains.
Question 3.
What are the basic mechanisms of heat transfer? Discuss the importance of these mechanisms with reference to the atmosphere.
Answer:
There are three basic mechanisms of heat transfer:
Radiation,
Conduction, and
Convection.
1. Radiation: Radiation is the act of transmitting energy in the form of particles of electromagnetic waves. The process is similar to that of transmission of light from an electric bulb. There are two forms of radiations: solar radiation and terrestrial radiation. The atmosphere gets heated up, in fact, through terrestrial radiation and not by solar radiation.
2. Conduction: When two bodies of unequal temperatures are in contact with one another, there is a flow of energy in the form of heat from warmer to cooler body. The layer of air resting upon the warmer earth becomes heated by the process of conduction. The actual conduction during the course of the day affects only the lowest layer of the atmosphere.
3. Convection: Convection is the process of heat transfer caused by the dying circulatory movement of the fluid itself. It takes place due to difference in temperature, and hence in density, and the pull of gravity. Convection produces vertical movement. The horizontal movement of a similar nature is called advection.

Fig97: Convection circulation
A cyclic circulation helps in transforming the heat of lower layers to the upper layers of the atmosphere. This process of heating is convection.
Question 4.
How is the atmosphere heated? Discuss the role of terrestrial radiation in this process.
Answer:
The only source of heat for the earth or the atmosphere is the sun. But the sun does not heat the atmosphere directly. The solar radiation or energy emitted from the sun travels through space and reaches the earth’s surface in the form of insolation or incoming solar radiation. The incoming solar radiation has no significant role in heating the atmosphere. But it helps the earth’s surface. The earth, in turn, reradiates this energy in the form of terrestrial radiation.
Thus the earth functions as a transformer in an electric circuit, receiving energy in one state and transmitting it to another. The sun heats the earth and earth heats the atmosphere. Nearly 51 % of solar energy reaches the earth directly or indirectly. The sun emits short wave radiations to space. The earth, on the other hand, radiates it back in long waves. The terrestrial radiation warms up the layers of atmosphere above it by direct contact or through the transmission of heat by upward movement of air currents.

Fig.9.8: The annual radiation budget of the earth. Units are percentages of the total solar radiation received at the outer edge of the atmosphere.
Question 5.
How many shapes the sun has? Describe photosphere.
Answer:
The sun has three shapes: the core and the interior. The innermost portion of the sun is extremely hot and hence here hydrogen atoms combine to form a smaller number of heavier helium atoms. In this process, certain mass is converted into energy.
The Photosphere: Photosphere is the solar surface. The energy produced in the core reaches to this surface. Most of the sun’s energy comes from the photosphere and we see it as a solar disc. In the photosphere, there are granules that transport energy from the base of the photosphere to its surface. Sunspots are dark regions on the photospheres. They are formed due to strong magnetic fields. The energy is released in the form of x-ray and ultra-violet radiations from the sunspots.
Above the photosphere occurs the sun’s atmosphere. The lower part is chromosphere and the upper is the corona. They are visible only during solar eclipses. Corona exudes electromagnetic energy. These energy particles can be captured by earth’s magnetic field in the ionosphere and their interaction with gases produce the aurora.
