Updated NCERT Solutions for Class 11 Geography Chapter 8: Solar Radiation, Heat Balance and Temperature | Important Questions
Welcome, students! This guide will demystify Class 11 Geography Chapter 8: Solar Radiation, Heat Balance and Temperature. We'll break down complex concepts into simple, easy-to-remember points. Mastering this chapter is crucial for scoring well in board exams and building a strong foundation for competitive exams like CUET and UPSC.
Chapter NameSolar Radiation, Heat Balance and Temperature
SubjectGeography (Book 1: Fundamentals of Physical Geography)
Class11
BoardCBSE
Important TopicsInsolation, Aphelion, Perihelion, Heat Budget of the Earth, Albedo, Temperature Inversion, Isotherms.
Difficulty LevelModerate (Conceptual understanding is key)
Exam Weightage3-5 Marks (Can be combined with other climatology chapters for long answer questions)
Learning Objectives
After completing this chapter, students will be able to:
- Explain the concept of solar radiation and the factors affecting its distribution.
- Understand the heating and cooling processes of the Earth's atmosphere.
- Describe the Heat Budget of the Earth and why our planet maintains a stable temperature.
- Analyse the factors that control the distribution of temperature across the globe.
- Define and explain phenomena like temperature inversion and isotherms.
Key Concepts and Definitions
Here are the most important terms you must know from this chapter.
- Insolation: A short form for Incoming Solar Radiation. It is the energy received by the earth from the sun.
- Aphelion: The position of the earth when it is farthest from the sun (around 4th July). During this time, the earth receives slightly less solar radiation.
- Perihelion: The position of the earth when it is nearest to the sun (around 3rd January). During this time, the earth receives slightly more solar radiation.
- Albedo: The percentage of solar radiation reflected back from a surface into space. Fresh snow has a high albedo, while a dark, wet field has a low albedo.
- Conduction: The transfer of heat through direct contact between two objects. It's most effective in the lower layers of the atmosphere.
- Convection: The transfer of heat through the vertical movement of a fluid (like air). Hot air rises, cools, and sinks, creating a convectional current.
- Advection: The horizontal transfer of heat by the movement of air (wind).
- Heat Budget of the Earth: The perfect balance between the incoming solar radiation absorbed by the Earth and the outgoing terrestrial radiation emitted by it. This balance is what keeps the Earth from getting progressively hotter or colder.
- Temperature Inversion: A situation where the normal temperature pattern is reversed. Instead of temperature decreasing with height, it starts increasing. This often happens on calm, long winter nights.
- Isotherms: Imaginary lines on a map connecting points that have the same temperature at a given time or for a certain period.
Full NCERT Solutions for Class 11 Geography Chapter 8
Here are the complete solutions to the exercises given at the end of your NCERT textbook chapter.
1. 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
Answer: (c) 23.5° N. This latitude is the Tropic of Cancer. On 21st June, the Northern Hemisphere is tilted towards the sun, and this day is known as the summer solstice in the Northern Hemisphere.
(ii) In which of the following cities, are the days the longest?
(a) Tiruvanantapuram
(b) Chandigarh
(c) Hyderabad
(d) Nagpur
Answer: (b) Chandigarh. The duration of the day increases as we move away from the Equator towards the poles in summer. Out of the given options, Chandigarh is located at the highest latitude (farthest from the equator), hence it will have the longest day during the summer solstice period.
(iii) The atmosphere is mainly heated by the:
(a) Short wave solar radiation
(b) Long wave terrestrial radiation
(c) Reflected solar radiation
(d) Scattered solar radiation
Answer: (b) Long wave terrestrial radiation. The incoming solar radiation (short waves) heats the Earth's surface. The Earth then radiates this heat back into the atmosphere in the form of long waves (terrestrial radiation). Greenhouse gases like carbon dioxide trap this outgoing long-wave radiation, heating the atmosphere from below.
(iv) 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 days in summer than the equatorial.
(c) Subtropical areas are nearer to the oceanic areas than the equatorial locations.
(d) Subtropical areas are more in the northern hemisphere.
Answer: (a) Subtropical areas tend to have less cloud cover than equatorial areas. The equatorial region experiences heavy cloud cover and rainfall almost daily (convectional rainfall). These clouds reflect a significant portion of incoming solar radiation, preventing the surface from getting extremely hot. In contrast, subtropical zones often have clear skies, allowing more direct sunlight to reach the surface, leading to higher temperatures.
2. Answer the following questions in about 30 words.
(i) How does the unequal distribution of heat over the surface of the earth in the course of a year, cause variations in weather and climate?
Answer: The unequal distribution of heat creates pressure differences across the globe. High temperature leads to low pressure, and low temperature creates high pressure. Air flows from high-pressure areas to low-pressure areas, creating winds. This movement of air, along with the transfer of heat and moisture, drives global weather patterns and determines the long-term climate of different regions.
(ii) What are the factors that control the distribution of temperature over the surface of the earth?
Answer: The primary factors controlling temperature distribution are:
- Latitude: Temperature decreases as we move from the equator to the poles.
- Altitude: Temperature decreases with an increase in height.
- Distance from the Sea: Coastal areas have moderate temperatures (maritime effect), while interior areas have extreme temperatures (continentality).
- Ocean Currents: Warm and cold ocean currents influence the temperature of coastal areas.
- Prevailing Winds: Winds transfer heat from one region to another.
(iii) In what way does the atmosphere get heated?
Answer: The atmosphere is primarily heated by outgoing long-wave terrestrial radiation. The Earth's surface absorbs short-wave solar radiation and heats up. It then radiates this energy back as long-wave infrared radiation. This outgoing heat is trapped by greenhouse gases (like CO2, water vapour), heating the lower atmosphere from below. Other minor processes include conduction and convection.
3. Answer the following questions in about 150 words.
(i) How is the unequal distribution of temperature over the surface of the earth responsible for the creation of pressure differences? Explain with a diagram.
Answer: The relationship between temperature and air pressure is fundamental to understanding weather and climate.
This difference in pressure is the primary driver of wind. Air always moves from an area of high pressure to an area of low pressure, trying to balance the pressure difference. This horizontal movement of air is what we call wind. Therefore, the unequal distribution of temperature directly leads to the creation of pressure belts, which in turn generate the global wind systems that regulate our planet's climate.
(Guidance for students: For this answer in your exam, draw a simple diagram showing a warm surface with rising air labeled "Low Pressure" and a cold surface with sinking air labeled "High Pressure." Draw an arrow on the ground moving from the High-Pressure area to the Low-Pressure area and label it "Wind".)
- Heating and Expansion: When a region's surface gets intensely heated by solar radiation, the air in contact with it also gets heated. Heated air expands, becomes less dense, and starts to rise.
- Creation of Low Pressure: As the air rises, it exerts less pressure on the surface below. This creates a region of Low Pressure (L.P.). Equatorial regions, which receive intense sunlight year-round, are a classic example of a low-pressure belt.
- Cooling and Contraction: In contrast, in cold regions, the air near the surface cools down. Cold air is dense and heavy, so it tends to sink.
- Creation of High Pressure: As the cold, dense air sinks, it exerts more pressure on the surface, creating a region of High Pressure (H.P.). The polar regions are permanent high-pressure zones.
This difference in pressure is the primary driver of wind. Air always moves from an area of high pressure to an area of low pressure, trying to balance the pressure difference. This horizontal movement of air is what we call wind. Therefore, the unequal distribution of temperature directly leads to the creation of pressure belts, which in turn generate the global wind systems that regulate our planet's climate.
(Guidance for students: For this answer in your exam, draw a simple diagram showing a warm surface with rising air labeled "Low Pressure" and a cold surface with sinking air labeled "High Pressure." Draw an arrow on the ground moving from the High-Pressure area to the Low-Pressure area and label it "Wind".)
(ii) Explain the heat budget of the earth with a diagram.
Answer: The Earth's heat budget refers to the perfect balance between the incoming solar energy (insolation) and the outgoing heat radiated back into space. This balance ensures that the Earth maintains a stable average temperature.
Let's assume the total incoming solar radiation is 100 units. Here’s how it's budgeted:
Reflection and Scattering (Albedo):
Absorption:
This perfect balance is the Earth's heat budget. It demonstrates how the Earth maintains a constant overall temperature over long periods.
(Guidance for students: A diagram is essential for this answer. Draw the Sun, Earth, and its atmosphere. Use arrows to show the 100 units coming in, and then break it down into the 35 units reflected and the 65 units absorbed (14 by atmosphere, 51 by surface). Then, show the 65 units being radiated back out.)
Let's assume the total incoming solar radiation is 100 units. Here’s how it's budgeted:
Reflection and Scattering (Albedo):
- About 35 units are reflected back to space even before reaching the Earth's surface.
- 27 units are reflected by clouds.
- 6 units are scattered by atmospheric particles.
- 2 units are reflected by the Earth's surface (like snow and ice).
Absorption:
- The remaining 65 units are absorbed.
- 51 units are absorbed by the Earth's surface (oceans, land).
- 14 units are absorbed by the atmosphere (water vapour, dust, ozone).
- To maintain a balance, the Earth must radiate back these 65 units.
- The Earth's surface radiates back 51 units as terrestrial radiation.
- 17 units are radiated directly into space.
- 34 units are absorbed by the atmosphere.
- The atmosphere, having absorbed 14 units from insolation and 34 units from terrestrial radiation (total 48 units), radiates these 48 units back into space.
- The total radiation returned to space is 17 (from Earth's surface) + 48 (from atmosphere) = 65 units.
- Incoming absorbed energy (65 units) = Outgoing radiated energy (65 units).
This perfect balance is the Earth's heat budget. It demonstrates how the Earth maintains a constant overall temperature over long periods.
(Guidance for students: A diagram is essential for this answer. Draw the Sun, Earth, and its atmosphere. Use arrows to show the 100 units coming in, and then break it down into the 35 units reflected and the 65 units absorbed (14 by atmosphere, 51 by surface). Then, show the 65 units being radiated back out.)
Extra Important Questions (Board Exam Style 2026-27)
Here are some extra questions to boost your preparation for the CBSE Class 11 exams.
Multiple Choice Questions (MCQs)
1. The fraction of solar energy reflected from the Earth into space is known as:
(a) Insolation
(b) Advection
(c) Albedo
(d) Conduction
Answer: (c) Albedo.
2. Temperature Inversion is most likely to occur during:
(a) A cloudy summer afternoon
(b) A windy, rainy day
(c) A long, calm winter night
(d) A hot, dry desert day
Answer: (c) A long, calm winter night.
3. The transfer of heat through the horizontal movement of air is called:
(a) Convection
(b) Advection
(c) Radiation
(d) Conduction
Answer: (b) Advection.
4. Isotherms are lines joining places of equal ________.
(a) Pressure
(b) Rainfall
(c) Temperature
(d) Humidity
Answer: (c) Temperature.
Short Answer Questions (2-3 Marks)
5. Differentiate between Aphelion and Perihelion.
Answer:
- Aphelion: This is the point in Earth's orbit where it is farthest from the Sun (approx. 152 million km). It occurs around July 4th.
- Perihelion: This is the point in Earth's orbit where it is closest to the Sun (approx. 147 million km). It occurs around January 3rd.
6. Why are the isotherms over oceans in the Northern Hemisphere more widely spaced and straighter compared to those over continents?
Answer: Isotherms are more regular over oceans because water has a high specific heat capacity. It heats up and cools down much more slowly than land. This moderating effect leads to less temperature variation over oceans. Continents, on the other hand, heat up and cool down rapidly, causing significant temperature differences and making the isotherms highly irregular and closely packed.
7. What is 'continentality'? How does it affect temperature?
Answer: 'Continentality' is the effect that the distance from the sea has on the climate of a location. Places far from the sea, in the interior of continents, do not experience the moderating influence of the ocean. As a result, they have very hot summers and very cold winters, leading to a high annual range of temperature.
8. Why does the atmosphere get heated from below?
Answer: The atmosphere is largely transparent to incoming short-wave solar radiation. This radiation passes through and heats the Earth's surface. The heated Earth then emits long-wave terrestrial radiation. Greenhouse gases in the lower atmosphere trap this outgoing long-wave heat, thus heating the atmosphere from the ground up.
Long Answer Questions (5 Marks)
9. Explain the five major factors that control the temperature distribution on the surface of the Earth.
Answer: The distribution of temperature across the globe is uneven. The five main factors controlling this distribution are:
- Latitude: Due to the curvature of the Earth, the angle of the sun's rays varies with latitude. At the equator, the rays are almost vertical, concentrating heat in a small area. As we move towards the poles, the rays become more slanted, spreading the same energy over a larger area, resulting in lower temperatures.
- Altitude: The atmosphere is heated by terrestrial radiation from below. Therefore, as we go higher in the troposphere, the temperature decreases. This is why high-altitude places like Shimla are colder than plains like Delhi, even if they are at similar latitudes. The rate of decrease is called the normal lapse rate.
- Distance from the Sea (Continentality): Land heats up and cools down faster than water. Coastal areas, influenced by the sea, have moderate temperatures with a low annual range (maritime climate). Inland areas have extreme temperatures with a high annual range (continental climate).
- Ocean Currents: Warm ocean currents, like the North Atlantic Drift, bring warmth to cold coastal areas, raising their temperature. Cold ocean currents, like the Labrador Current, cool down the adjacent coastal regions.
- Prevailing Winds and Air Masses: Winds that blow from the sea to the land (onshore winds) bring a moderating influence. Winds blowing from hot regions increase the temperature, while those from cold regions lower it. Air masses also retain the temperature characteristics of their source region.
10. What is a Temperature Inversion? Explain its formation and its effects on weather.
Answer: Temperature inversion is an atmospheric condition in which the temperature, instead of decreasing with altitude, increases. A layer of warm air sits on top of a layer of cooler air near the ground.
Formation:
A temperature inversion commonly forms during long, calm winter nights with clear skies.
Formation:
A temperature inversion commonly forms during long, calm winter nights with clear skies.
- Rapid Cooling: The ground loses heat quickly through terrestrial radiation.
- Cooling of Lower Air: The layer of air in direct contact with the cold ground also cools down through conduction.
- Warmer Upper Air: The air just above this layer does not cool as quickly and remains relatively warm.
- Inversion Layer: This results in a situation where cold, dense air is trapped below a layer of warm, less dense air.
- Stability: The inversion creates extremely stable atmospheric conditions, as the cold, heavy air at the bottom cannot rise.
- Fog and Smog: It traps dust, smoke, and other pollutants near the ground, leading to the formation of dense fog and smog, which can severely reduce visibility and cause respiratory problems in cities.
- Frost: On calm nights, if the temperature near the ground drops below freezing point, it can lead to the formation of frost, which is harmful to crops.
- Limits Cloud Formation: The stability caused by inversion suppresses convection, preventing the formation of clouds and potential rainfall.
Case-Based / Source-Based Question
11. Instructions: Read the passage below and answer the questions that follow.
The Earth's albedo plays a crucial role in regulating its temperature. Surfaces like ice and snow are highly reflective, sending a large portion of solar radiation back into space. Forests and oceans, being darker, absorb more energy. A feedback loop exists where rising global temperatures cause ice caps to melt. This reduces the planet's overall albedo as the darker ocean or land is exposed. The exposed darker surface absorbs more solar radiation, leading to further warming and more ice melt. This phenomenon is known as the ice-albedo feedback.
(i) What is albedo?
Answer: Albedo is the measure of how much solar radiation is reflected by a surface, expressed as a percentage.
(ii) Which surface mentioned in the passage has the highest albedo?
Answer: Ice and snow have the highest albedo.
(iii) Explain the 'ice-albedo feedback' loop in your own words.
Answer: The 'ice-albedo feedback' is a cycle where warming temperatures melt ice. The exposed darker surface (land or ocean) absorbs more heat than the reflective ice, causing even more warming, which in turn melts more ice. It's a positive feedback loop that accelerates global warming.
Common Mistakes Students Make
- Confusing Insolation with Temperature: Insolation is the cause (incoming energy), while temperature is the effect (the degree of heat). A place can receive high insolation but have moderate temperature due to factors like cloud cover (e.g., the equator).
- Mixing up Conduction, Convection, and Advection:
- Conduction: Heat transfer by touch (air touching the hot ground).
- Convection: Vertical movement of heat (hot air rising).
- Advection: Horizontal movement of heat (winds).
- Not Explaining the Heat Budget with Numbers: When asked about the heat budget, simply stating "income = outflow" is not enough. You must use the approximate values (100 units in, 35 reflected, 65 absorbed and then radiated back) to score full marks.
- Forgetting to Draw Diagrams: Questions on Heat Budget, Pressure Belts, and Temperature Inversion become much easier to explain and score higher with a simple, well-labeled diagram.
Exam Preparation Tips for 2026-27
- Focus on Concepts: This is a conceptual chapter. Don't just memorize definitions. Understand why temperature varies and how the heat balance works.
- Master the Heat Budget Diagram: Practice drawing and labeling the heat budget diagram. It's a frequently asked long-answer question.
- Use Flowcharts: For processes like the heating of the atmosphere or the formation of temperature inversion, create simple flowcharts to aid memory.
- Relate to Real Life: Think about why Shimla is cold (altitude), why Mumbai has a moderate climate (distance from the sea), and why deserts are so hot during the day (lack of clouds, low albedo of sand).
- Last-Minute Revision: Before the exam, quickly revise the key definitions (Albedo, Isotherm, Inversion), the Heat Budget values, and the five factors affecting temperature.
Frequently Asked Questions (FAQs)
Q1: What is the Heat Budget of Earth Class 11?
The Heat Budget of Earth is the balance between the amount of solar energy absorbed by the Earth (65%) and the amount of heat radiated back into space. This perfect balance ensures that the Earth's average temperature remains stable over time.
Q2: Why is the atmosphere heated by terrestrial radiation and not directly by the sun?
The atmosphere is largely transparent to the sun's incoming short-wave radiation. However, it is very effective at absorbing the outgoing long-wave (infrared) radiation emitted by the heated surface of the Earth, thus heating the atmosphere from below.
Q3: What are the three main ways the atmosphere gets heated?
The three mechanisms are Radiation (heating from terrestrial radiation), Conduction (air in contact with the warm ground gets heated), and Convection (vertical transfer of heat as warm air rises).
Q4: Why is it hotter at the Tropic of Cancer/Capricorn than at the Equator?
While the Equator receives direct sunlight, it also has heavy cloud cover year-round, which reflects a lot of solar energy. The subtropical regions (near the Tropics) have clearer skies, allowing more direct, uninterrupted sunlight to reach and heat the surface, often resulting in higher temperatures.
Q5: What are isotherms and why are they important?
Isotherms are imaginary lines on a map connecting places with the same temperature. They are important because they help us visualize the horizontal distribution of temperature across the globe and understand the influence of factors like latitude, continents, and oceans on temperature patterns.
Conclusion: Congratulations on completing this detailed guide for "Solar Radiation, Heat Balance and Temperature"! By understanding these core concepts, you've built a strong foundation in climatology. Remember, geography is not just about memorization but about understanding the processes that shape our world. Revise these notes regularly, practice the extra questions, and analyze previous years' question papers (PYQs) to master the chapter. Keep up the great work!