NCERT Solutions for Class 11 Geography Chapter 8 - Solar Radiation, Heat Balance and Temperature

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    90. Multiple choice questions.

    (i) The sun is directly overhead at noon on 21st June at:

    (a) The equator

    (b) 23.5° S

    (c) 23.5° N

    (d) 66.5° N

    Ans. (c) 23.5° N

    (ii) In which one of the following cities, are the days the longest?

    (a) Tiruvanantpuram

    (b) Chandigarh

    (c) Hyderabad

    (d) Nagpur

    Ans. (b) Chandigarh

    (iii) The atmosphere is mainly heated by the:

    (a) Short wave solar radiation

    (b) Reflected solar radiation

    (c) Long wave terrestrial radiation

    (d) Scattered solar radiation

    Ans. (c) Long wave terrestrial radiation.

    (iv) Make correct pairs from the following two columns. 

    Column I
    Column II
    (a) Insolation i. The difference between the mean temperature of the warmest and the coldest months.
    (b) Albedo ii. The lines joining the places of equal temperature.
    (c) Isotherm iii. The incoming solar radiation.
    (d) Annual range iv. The percentage of visible light reflected by an object.

    Ans. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i).

    (v) The main reason that the earth experiences highest temperatures in the subtropics in the northern hemisphere rather than at the equator is:

    (a) Subtropical areas tend to have less cloud cover than equatorial areas.

    (b) Subtropical areas have longer day hours in the summer than the equatorial.

    (c) Subtropical areas have an enhanced “green house effect” compared to equatorial areas.

    (d) Subtropical areas are nearer to the oceanic areas than the equatorial locations.

    Ans. (a) Subtropical areas tend to have less cloud cover than equatorial areas.

    91. Answer the following questions in about 30 words.

    (i) How does the unequal distribution of heat over the planet earth in space and time cause variations in weather and climate?

    Ans. The sun provides almost all of the energy that the earth needs. The energy that the earth receives from the sun is then radiated back into space. As a result, throughout time, neither the earth’s temperature rises nor falls. As a result, not all regions of the globe experience the same amount of heat. This variation causes pressure difference in the atmosphere. As a result, heat is transferred by winds from one area to another. Thus, differences in weather and climate are brought on by the uneven distribution of heat over the globe Earth in both space and time.

    (ii) What are the factors that control temperature distribution on the surface of the earth?

    Ans. The factors that cause these variations in insolation are:

    (a) The rotation of earth on its axis.

    (b) The angle of inclination of the sun’s rays.

    (c) The length of the day.

    (d) The transparency of the atmosphere.

    (e) The configuration of land in terms of its aspect.

    (iii) In India, why is the day temperature maximum in May and why not after the summer solstice?

    Ans. Tropic of Cancer on June 21(summer solstice) India has started receiving its monsoon. It brings cooling effect to the climate of India, which was facing intense heat since March. As a result, the day temperature maximum in May and why not after the summer solstice.

    (iv) Why is the annual range of temperature high in the Siberian plains?

    Ans. Because the Siberian Plains are positioned far from the ocean and equalising effect of ocean is relatively minimal, and this plains have a continental climate. As a result, the annual range of temperature remains high in the Siberian plains.

    92. Answer the following questions in about 150 words.

    (i) How do the latitude and the tilt in the axis of rotation of the earth affect the amount of radiation received at the earth’s surface?

    Ans. The sun has a significant impact on the quantity of insolation received at various latitudes when the earth’s axis forms an angle of 66.5 degrees with the plane of its orbit around the sun. Because of its inclination toward the sun in the month of June, the Northern Hemisphere experiences more solar radiation than the Southern Hemisphere.

    Due to its inclination toward the sun in the month December, the southern hemisphere experiences more solar radiation than the northern hemisphere. The amount of heat produced by solar radiation on earth varies with latitude. For the majority of the year, the sun’s beams are practically vertical near the equator and at the poles. As a result, areas close to the equator experience greater solar radiation than those close to the poles.

    (ii) Discuss the processes through which the earthatmosphere system maintains heat balance.

    Ans. The earth-atmosphere system maintains heat balance in different ways of heating and cooling of the atmosphere:

    (a) Conduction:

    1. After being heated by insolation, the earth radiates heat in the form of long waves in to the nearby atmospheric layers. The top layers in touch with the lower layers and the air in contact with the land both gradually warm up.
    2. Energy flows from the warmer to the colder body when two bodies of different temperatures come into contact with one another. Heat is transferred until both bodies reach the same temperature or the contact is severed, whichever comes first.

    (b) Convection : The air in contact with the earth rises vertically on heating in the form of currents and further transmits the heat of the atmosphere. This process of vertical heating of the atmosphere is known as convection. The convective transfer of energy is confined only to the troposphere


    (a) Advection is the term used to describe the transmission of heat by horizontal air movement. The air’s horizontal movement is generally more significant than its vertical movement.

    (b) In middle latitudes, advection alone is responsible for the majority of diurnal (day and night) variation in daily weather. Local winds known as “loo” are the result of the advection process and occur in tropical places, particularly in northern India during the summer.

    (iii) Compare the global distribution of temperature in January over the northern and the southern hemisphere of the earth.

    Ans. The temperature distribution is generally shown on the map with the help of isotherms, the joining places having equal temperature.

    (a) In general, the isotherms run parallel to the latitude.

    (b) The land surface area in the northern hemisphere is significantly larger than in the southern hemisphere. As a result, the effects of land mass and ocean currents are quite noticeable.

    (c) The isotherms diverge in January, moving to the north over the ocean and to the south over land. On the North Atlantic Ocean, this can be seen.

    (d) The Gulf Stream and North Atlantic Drift, which are warm ocean currents, warm up the Northern Atlantic Ocean and cause the isotherms to curve toward the north. In Europe, the isotherms bend southward over the terrain as temperatures drop suddenly.

    (e) In the Southern Hemisphere, the influence of the ocean is very noticeable. Compared to the Northern Hemisphere, the temperature variation is more gradual here since the isotherms are more or less parallel to the latitudes.

    (f) The isotherm of 20°C, 10°C, and 0°C corresponds to latitudes of 35°S, 45°S, and 60°S, respectively.

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