GEOGRAPHY- CLASS-11: FUNDAMENTALS OF PHYSICAL GEOGRAPHY
CHAPTER-8
Solar Radiation, Heat Balance and Temperature
1. Multiple Choice Questions
(i) The sun is directly overhead at noon on 21st June at:
Answer: (c) 23.5° N
Explanation: On 21st June (Summer Solstice), the Sun is directly overhead at the Tropic of Cancer (23.5° N).
(ii) In which one of the following cities are the days the longest?
Answer: (b) Chandigarh
Explanation: Chandigarh is located farthest north among the given cities. On 21st June, places at higher northern latitudes experience longer days.
(iii) The atmosphere is mainly heated by the:
Answer: (c) Long wave terrestrial radiation
Explanation: The Earth's surface absorbs solar radiation and re-radiates it as long-wave terrestrial radiation, which heats the atmosphere.
(iv) Make correct pairs from the following two columns.
| Column I | Column II |
|---|---|
| Insolation | (c) The incoming solar radiation |
| Albedo | (d) The percentage of visible light reflected by an object |
| Isotherm | (b) The lines joining the places of equal temperature |
| Annual range | (a) The difference between the mean temperature of the warmest and the coldest months |
Correct Answer: (i) → (c), (ii) → (d), (iii) → (b), (iv) → (a)
2. 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?
Answer:
The Earth receives unequal solar energy because of its spherical shape and tilted axis. This creates differences in temperature and pressure, resulting in variations in winds, rainfall, weather and climate.
(ii) What are the factors that control temperature distribution on the surface of the Earth?
Answer:
The main factors are latitude, altitude, distance from the sea, ocean currents, prevailing winds, slope and aspect of land, cloud cover, and nature of the Earth's surface.
(iii) In India, why is the day temperature maximum in May and why not after the summer solstice?
Answer:
In May, clear skies and dry conditions allow maximum heating of the land. After the summer solstice, the arrival of the southwest monsoon brings clouds and rainfall, reducing daytime temperatures.
(iv) Why is the annual range of temperature high in the Siberian plains?
Answer:
The Siberian Plains are far from the sea and have a continental climate. Summers are warm and winters are extremely cold, resulting in a very high annual range of temperature.
3. 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?
Answer:
Latitude greatly influences the amount of solar radiation received on the Earth's surface. Near the Equator, the Sun's rays fall almost vertically throughout the year, concentrating more heat over a smaller area. Towards the poles, the rays strike obliquely, spreading the same amount of energy over a larger area and reducing heating. The Earth's axis is tilted at an angle of 23½°, which causes seasonal changes. During one part of the year, the Northern Hemisphere is tilted towards the Sun and receives more direct sunlight, resulting in summer. At the same time, the Southern Hemisphere receives less sunlight and experiences winter. Six months later, the situation reverses. Thus, latitude determines the angle of the Sun's rays, while the Earth's axial tilt causes seasonal variations in the amount and duration of solar radiation received.
(ii) Discuss the processes through which the Earth-atmosphere system maintains heat balance.
Answer:
The Earth-atmosphere system maintains heat balance through the continuous exchange of energy. The Sun supplies short-wave solar radiation, known as insolation. A portion of this radiation is reflected back into space by clouds, atmospheric particles and the Earth's surface. The remaining energy is absorbed by the land, oceans and atmosphere. The heated Earth then emits long-wave terrestrial radiation. Greenhouse gases absorb part of this outgoing radiation and re-radiate it, helping to maintain a suitable temperature. Heat is also transferred through conduction, convection and advection. Ocean currents and winds redistribute heat from warmer regions to colder regions. This constant movement of energy ensures that the Earth neither becomes excessively hot nor excessively cold, maintaining the global heat balance.
(iii) Compare the global distribution of temperature in January over the northern and the southern hemisphere.
Answer:
In January, the Northern Hemisphere experiences winter, while the Southern Hemisphere experiences summer. The Northern Hemisphere records very low temperatures over large continental areas such as Siberia, Canada and Greenland because land cools rapidly. Isotherms are irregular due to the unequal distribution of land and water. In contrast, the Southern Hemisphere has higher temperatures because it is summer there. Since this hemisphere is dominated by oceans, temperatures remain more moderate and isotherms are comparatively straight and evenly spaced. The oceanic influence reduces temperature contrasts between regions. Therefore, January shows a much greater variation of temperature in the Northern Hemisphere than in the Southern Hemisphere.