Selina Concise Solutions for ICSE Class 9 Geography Chapter 13 Insolation

Exercises

I. Short Answer Questions.

Question 1. What is solar radiation ? What is its significance for the earth ?
Answer: The sun continuously radiates heat and light energy in all the directions. It is known as solar radiation. Solar radiation is the only primary source of light and heat on the earth. The earth receives its heat from solar radiation which is a tiny fraction of the radiated energy of the sun.
In simple words: Solar radiation is the energy the sun sends out in every direction as light and heat. It is the most important power source for our planet, giving plants the energy to grow and keeping us warm.

📝 Teacher's Note: Use the analogy of a giant lightbulb in space that never turns off. Explain that while the Sun produces massive energy, Earth only receives a very small, safe portion of it.

🎯 Exam Tip: To get full marks, define solar radiation as the "primary source" of heat and light on Earth.

Question 2. What is meant by insolation ? State two of its main characteristics.
Answer: The amount of solar energy received by the earth is called insolation, but only one part out of two billion parts reaches the earth. So, out of total \( 100\% \) solar energy only \( 51\% \) reaches the earth, \( 35\% \) reflected back to into space and only \( 14\% \) is absorbed by the ozone layer.
In simple words: Insolation is short for "Incoming Solar Radiation." It is the actual amount of sun energy that hits the Earth, though much of it is reflected away by clouds or absorbed by our atmosphere.

📝 Teacher's Note: Explain the origin of the word: IN-coming SOL-ar radi-ATION. Use the percentage breakdown provided in the answer to show where the energy is lost.

🎯 Exam Tip: Remember the breakdown: \( 51\% \) reaches Earth, \( 35\% \) reflects, and \( 14\% \) is absorbed by the ozone layer.

Question 3. State two advantages of convectional heating of the atmosphere.
Answer: Convectional heating of the atmosphere is done by heating up the layer of air touching land surface and rising up to warm up the upper layer, while the cold wind sinks down and again heated up by the terrestrial radiation. This circulation causes formation of clouds, rainfall and mild changes in climatic behaviour.
In simple words: Convectional heating is a cycle where warm air rises and cool air sinks. This constant movement helps create clouds and brings the rain we need for life.

📝 Teacher's Note: Compare this to a pot of soup on a stove; the hot soup rises from the bottom and the cooler soup sinks, creating a mixing cycle.

🎯 Exam Tip: Focus on keywords like "circulation," "formation of clouds," and "rainfall" when describing the advantages.

Question 4. Name four factors that affect the temperature of a place.
Answer: The four factors that affect the temperature of a place are :
1. Latitude
2. Distance from the sea.
3. Altitude
4. Wind direction
5. Natural vegetation
In simple words: Many things decide if a place is hot or cold, such as how far it is from the equator (latitude), how high it is in the mountains (altitude), or if it is near the ocean.

📝 Teacher's Note: Ask students why hill stations are cooler than cities on the plains to introduce the concept of "Altitude."

🎯 Exam Tip: You can choose any four points from the five listed to score full marks.

Question 5. How does the distance from the sea affect the distribution of temperature ?
Answer: Due to the physical property of water, which is heated up and cooled down slowly with respect to the land. So, the coastal areas experience mild climate with least range of temperature, while the regions far from the sea are affected by extreme climate with maximum range of temperature.
In simple words: Land heats up and cools down much faster than the ocean. Because the ocean stays at a steady temperature longer, it keeps the air in coastal cities mild, while inland cities get very hot summers and very cold winters.

📝 Teacher's Note: Use the example of a hot beach: the sand might burn your feet, but the water feels cool. This shows how land and water heat up differently.

🎯 Exam Tip: Use the term "mild climate" for coastal areas and "extreme climate" for inland areas to impress the examiner.

Question 6. State the pattern of temperature in mid latitudes.
Answer: Due to spherical shape of the earth, temperature zone gets less insolation resulting in moderate climate with normal temperature ranging from \( 15^\circ C \) to \( 30^\circ C \). The duration of sunshine is greater in summer than winter. So the summer is warm and winter is cold.
In simple words: In the middle parts of the Earth, the climate is moderate because the sun's rays aren't as direct as at the equator. These areas have clear seasons with warm summers and cold winters.

📝 Teacher's Note: Explain that "Mid latitudes" are the regions between the hot tropics and the freezing poles. This is often called the "Temperate Zone."

🎯 Exam Tip: Mention the temperature range \( 15^\circ C \) to \( 30^\circ C \) as a characteristic of this zone.

Question 7. How would the breezes that blow during the day and those that blow during the night affect the temperature of a place situated in the coastal region ?
Answer: During the day the sea breeze blowing from sea towards land keeps the coastal region cool and during the night land breeze blowing from land towards sea makes the sea cooler. This interchange of breeze maintains the heat balance resulting in the mild climate of the coastal regions with lower daily and annual ranges of temperature.
In simple words: During the day, cool air from the sea keeps the land from getting too hot. At night, the breeze blows from the land to the sea, helping the whole area stay at a comfortable temperature.

📝 Teacher's Note: Draw a simple arrow diagram showing air moving from sea to land (Day) and land to sea (Night) to help visual learners.

🎯 Exam Tip: Clearly distinguish between "Sea Breeze" (Day) and "Land Breeze" (Night).

Question 8. What difference is there in the temperatures on a mountain and on a sea shore ?
Answer: The rate of decrease of temperature is \( 1^\circ C \) for every \( 166 \text{ metres} \), the temperatures on a mountain are for lesser than the temperatures on a sea shore which is nearly at zero height.
In simple words: High mountains are much colder than the beach because temperature drops as you go higher up. For every \( 166 \text{ meters} \) you climb, the air gets \( 1^\circ C \) cooler.

📝 Teacher's Note: Remind students of the "Normal Lapse Rate" they learned previously. It is the reason why mountains can have snow even in tropical countries.

🎯 Exam Tip: Always include the specific figure: \( 1^\circ C \) for every \( 166 \text{ metres} \) to show precision.

Question 9. Why is India cooler in December than in July ?
Answer: Tropic of Cancer passes midway across India, so, there is summer season in July, while in December the sun is vertical on the Tropic of Capricorn in southern hemisphere, so India experiences winter season. So naturally December is cooler than July.
In simple words: In July, the Sun shines more directly over India, making it hot summer. In December, the Sun shines more directly on the southern half of the world, so India gets less direct heat and enters winter.

📝 Teacher's Note: Use a globe and a flashlight to show how the tilt of the Earth changes which hemisphere gets direct "vertical" sun rays.

🎯 Exam Tip: Mention the "Tropic of Cancer" and "Tropic of Capricorn" to explain the position of the sun during different seasons.

Question 10. State two chief characteristics of the Temperate zone.
Answer: Medium temperature and medium rainfall due to slanting rays of the sun and less evaporation.
In simple words: The Temperate zone has balanced weather because the sun's rays hit the ground at an angle. This means it doesn't get as hot as the tropics, so there is less evaporation and moderate rain.

📝 Teacher's Note: Contrast this with the "Frigid Zone" where rays are extremely slanting and the "Torrid Zone" where they are vertical.

🎯 Exam Tip: The core points are "slanting rays" and "medium temperature/rainfall."

Question 11. Explain the following:
(a) Diurnal range of temperature.
(b) Mean Monthly Range of Temperature.
(c) Mean Annual Range of Temperature.
Answer:
(a) Diurnal range is the difference between the maximum and minimum temperature within \( 24 \text{ hours} \), of the day.
(b) It is the difference between the mean maximum and mean minimum temperatures within the month.
(c) It is the difference between mean maximum and mean minimum temperatures within a year, mainly between June and January.
In simple words: These are ways to measure temperature change. "Diurnal" looks at a single day, "Monthly" looks at a month, and "Annual" looks at the hottest and coldest months of the whole year.

📝 Teacher's Note: Practice calculation with the students: if today's high is \( 35^\circ C \) and low is \( 20^\circ C \), the diurnal range is \( 15^\circ C \).

🎯 Exam Tip: For all three definitions, the keyword is "difference between maximum and minimum."

Question 12. Define briefly ‘Heat Balance”.
Answer: Heat balance is defined as the state of equilibrium that exists on earth between incoming insolation from the sun and the out going terrestrial radiation from the earth.
In simple words: Heat balance is like a budget. The Earth must send out as much energy as it gets from the sun so it doesn't get hotter and hotter every day.

📝 Teacher's Note: Use a bank account analogy: if you earn \$100 and spend \$100, your balance stays the same. The Earth "spends" exactly what it "earns" in solar energy.

🎯 Exam Tip: Use the word "equilibrium" to describe the balance between incoming and outgoing heat.

Question 13. Name the heat zones of the earth.
Answer: Torrid zone, Temperate zone and Frigid zone.
In simple words: The Earth is divided into three temperature bands. The center is hot (Torrid), the top and bottom are icy (Frigid), and the middle areas are balanced (Temperate).

📝 Teacher's Note: Ask students to identify which zone their country falls into. This makes the global concept feel personal.

🎯 Exam Tip: List them in order from hottest to coldest or equator to poles for better structure.

II. Distinguish between each of the following

Question. Insolation and Terrestrial Radiation.
Answer:
Insolation :
1. It is the incoming solar radiation intercepted by the earth.
2. It travels in short waves.
3. Insolation involves only \( 51 \text{ units} \) out of \( 100 \text{ units} \) of solar radiation.
Terrestrial Radiation :
1. It is the earth’s radiation given back to atmosphere and space.
2. It travels in long waves.
3. Out of \( 51 \text{ units} \) of insolation \( 34 \text{ units} \) are transferred to the atmosphere and \( 17 \text{ units} \) go back to space.
In simple words: Insolation is the sun energy coming "in" as fast short waves. Terrestrial radiation is the energy the Earth sends "back" out into space as slower long waves.

📝 Teacher's Note: Explain that short waves come from hot objects (Sun), while long waves come from cooler objects (Earth). This is a fundamental rule of physics.

🎯 Exam Tip: Create a T-chart for distinction questions. Always contrast the "wave type" (short vs. long) as it's a key scientific difference.

Question. Land Breeze and Sea Breeze.
Answer:
Land Breeze :
1. It blows from Land to sea.
2. It blows at night.
3. It makes the sea water cooler.
4. It moderates the temperature of sea.
Sea Breeze :
1. It blows from sea to land.
2. It blows in the day time.
3. It makes coastal parts warmer
4. It moderates the climate of the coastal parts.
In simple words: Sea breeze is a cool "day wind" coming from the ocean. Land breeze is a "night wind" blowing from the cooling ground back to the water.

📝 Teacher's Note: Note that breeze is named after its *origin*. Sea breeze comes FROM the sea. Land breeze comes FROM the land.

🎯 Exam Tip: Remember: Sea Breeze = Day; Land Breeze = Night. Mixing these up is a common mistake.

Question. Torrid and Temperate Zones.
Answer:
Torrid Zone :
1. It lies between \( 23\frac{1}{2}^\circ \text{ N} \) and \( 23\frac{1}{2}^\circ \text{ S} \)
2. It receives highest temperature and rainfall.
3. It receives the vertical sun’s rays.
4. Equatorial region and the tropical belt receive maximum insolatioa
Temperate Zone :
1. It lies between \( 23\frac{1}{2}^\circ \text{ N} \text{ and } 66\frac{1}{2}^\circ \text{ N} \) & \( 23\frac{1}{2}^\circ \text{ S} \text{ and } 66\frac{1}{2}^\circ \text{ S} \)
2. It receives medium, temperature and rainfall.
3. It received slanting rays of sun.
4. Due to spherical shape of the earth, this zone received quite less amount of insolation.
In simple words: The Torrid zone is the center belt where the sun is right overhead and it's very hot. The Temperate zones are above and below the center where sun rays are slanted and the weather is milder.

📝 Teacher's Note: Use the provided latitude degrees to show where these zones start and end on a map. Note the typo "insolatioa" from the textbook.

🎯 Exam Tip: Use the term "vertical rays" for the Torrid zone and "slanting rays" for the Temperate zone.

Question. Annual Range and Monthly Range of Temperature.
Answer:
Annual Range of Temperature :
1. It is the difference between the highest and lowest temperatures within one year.
2. It is the difference between the highest temperature of May-June and lowest temperature in December January, i.e. the temperature difference between summer and winter.
Monthly range of Temperature :
1. It is the difference between the maximum and minimum temperatures within a month.
2. Mostly the middle of month is noted for maximum and end of the month records minimum temperatures.
In simple words: Annual range compares the hottest summer month to the coldest winter month. Monthly range compares the hottest day of a month to the coldest day of that same month.

📝 Teacher's Note: Explain that "Range" always means a subtraction calculation (Max - Min).

🎯 Exam Tip: For Annual range, mention that it represents the difference between "Summer and Winter" temperatures.

III. Give reasons for each of the following

Question 1. North India has a greater range of temperature than South India.
Answer: North India comes in temperate zone, while South India comes in Torrid Zone situated in the North and South of Tropic of Cancer. So North Indian places have greater range, which is greatest in the Desert of Rajasthan.
In simple words: South India is closer to the equator and surrounded by sea, keeping it warm all year. North India is far from the sea and further from the equator, so it gets very hot in summer and very cold in winter.

📝 Teacher's Note: Mention that the sea has a "moderating" effect. South India is like a peninsula, while North India is a vast landmass.

🎯 Exam Tip: Link the greater range to North India's "Temperate Zone" location and distance from the sea.

Question 2. The temperature of Delhi is less than that of Chennai in December.
Answer: Delhi is far from sea, while Chennai is situated along the coast of Bay of Bengal. So Delhi is colder than Chennai in December.
In simple words: In winter, the ocean near Chennai stays warm and keeps the city mild. Delhi is in the middle of land with no ocean nearby to warm the air, so it gets freezing cold.

📝 Teacher's Note: This is a real-world example of "Continentality" (inland extreme) versus "Maritime" (coastal mild) climate.

🎯 Exam Tip: Always contrast the "Coastal location" of Chennai with the "Inland location" of Delhi.

Question 3. Distance from the sea affects the temperature of a place.
Answer: Warm effect of sea keeps the temperature less in summer and higher in winter, e.g. Bombay (Mumbai) is wanner than Delhi in winter.
In simple words: The ocean acts like a giant temperature regulator. It prevents coastal cities like Mumbai from getting too hot in the summer or too cold in the winter.

📝 Teacher's Note: Note the typo "wanner" (warmer) from the text. This principle explains why island nations have very steady temperatures.

🎯 Exam Tip: Use the Mumbai/Delhi comparison to illustrate the difference between coastal and inland climates.

Question 4. Land is heated and cooled faster than the sea.
Answer: In the desert of Rajasthan range of temperature is highest due to the physical property of land to be heated and cooled down quickly with respect to the sea. So, the temperature difference is least at Mangalore and Chennai.
In simple words: Soil and rock (land) soak up heat instantly and lose it just as fast. Water is deep and moves around, so it takes a much longer time to change temperature.

📝 Teacher's Note: Remind students that land is "solid" and heats only the surface, while water allows heat to penetrate deeper and circulate.

🎯 Exam Tip: Mention that temperature difference is highest in deserts and least in coastal cities like Mangalore.

Question 5. The temperature of a place depends largely upon its latitude.
Answer: As the rays of the sun become more and more slanting with increasing latitudes. So the tropical region never gets snowfall, while the polar region is always frozen.
In simple words: At the equator, the sun hits the Earth straight on, which is very hot. As you move toward the poles, the sun's rays are spread out and hit at a slant, which provides much less heat.

📝 Teacher's Note: Use a flashlight: shine it straight at a wall (bright/hot) then at an angle (dimmer/cooler). This is how latitude works.

🎯 Exam Tip: Use the keyword "angle of incidence" or "slanting rays" to explain the drop in temperature toward the poles.

Question 6. Desert areas experience a high day temperature and a much lower night temperature.
Answer: Desert areas are covered with large sand plains. The physical property of the sand is to heated up quickly and cooled down abruptly ; so the day temperature is very high and the night temperature is very less.
In simple words: Sand is a very poor "battery" for heat. It gets burning hot under the sun but releases all its heat the second the sun goes down, leaving the night air cold.

📝 Teacher's Note: Also mention that deserts have very little water vapor in the air; water vapor acts as a blanket, so without it, heat escapes into space at night rapidly.

🎯 Exam Tip: Highlight the "abrupt cooling" of sand as the primary reason for cold desert nights.

Question 7. The ports of the western coast of Europe remain ice- free during winter.
Answer: Due to the warm effect of the Gulf Stream and North Atlantic Drift the ports of Western Europe remain ice free in winter to motivate successful international oceanic trade, e.g., London, Calais, Lisbon, Amsterdam, Brest, Le Havre etc.
In simple words: Huge warm water currents flow from the tropics toward Europe. This warm water acts like a heater for the coastline, preventing the harbors from freezing into solid ice.

📝 Teacher's Note: This is a great example of how "Ocean Currents" affect temperature. Without this current, London would be as icy as parts of Canada.

🎯 Exam Tip: Name the "Gulf Stream" and "North Atlantic Drift" to give a complete geographical explanation.

PQ. The earth’s surface receives only about 51% of the Solar energy.
Answer: Out of \( 100 \text{ units} \), only \( 51 \text{ units} \) are received by the earth as isolation, while \( 35 \text{ units} \) are reflected back by atmospheric layers, clouds, snowfields and \( 14 \text{ units} \) are absorbed by ozone layer.
In simple words: Almost half of the sun's energy never actually touches the ground! It is either bounced back into space by clouds and ice or soaked up by the atmosphere before it reaches us.

📝 Teacher's Note: This distribution is part of the "Heat Budget." Explain that reflection without heating is called "Albedo."

🎯 Exam Tip: Be ready to state exactly where the "lost" \( 49\% \) goes (\( 35\% \) reflection and \( 14\% \) absorption).

Question 8. The vertical rays of the sun give more insolation than the slanting rays.
Answer: Tropical region gets vertical rays of the sun and receive much heat providing high temperature while the temperate and polar regions have less temperature due to slanting rays of the sun.
In simple words: Vertical rays focus all their energy on a small spot, making it very hot. Slanting rays spread the same energy over a much larger area, making it feel weaker and cooler.

📝 Teacher's Note: Use the analogy of a magnifying glass: when held perfectly straight, it focuses heat; when tilted, the focus is lost. This is why the equator is hotter.

🎯 Exam Tip: Mention that vertical rays pass through a "shorter distance" in the atmosphere, so they lose less heat.

Question 9. A desert region has a high range of temperature than a forest region.
Answer: A desert region gets highly heated and quickly cooled down due to the sand cover; while the forested region most of the solar energy is used in transpiration in vegetation realm and do not become very hot. On the other hand due to the emission of carbon dioxide by plants the temperature is maintained due to the heat absorbing property of \( CO_2 \).
In simple words: In a forest, the trees "sweat" (transpiration) and provide shade, which keeps things cool. In a desert, the bare sand has nothing to stop it from getting scorching hot or freezing cold.

📝 Teacher's Note: Note that forests create their own "micro-climate." The moisture in the air from trees prevents the extreme temperature swings found in dry deserts.

🎯 Exam Tip: Contrast the "sand cover" of deserts with the "transpiration" in forested regions.

IV. Long Answer Questions

Question 1. Describe the four factors that affect the distribution of temperature.
Answer: The factors are different physical properties of land and water keeping continental climate cold and oceanic climate mild
Latitude The temperature decreases from the equator towards poles.
Distance from the sea keeping coastal ports mild and areas for from sea cold.
Altitude mountains are cooler than plains due to the lapse rate of decrease of temperature of \( 1^\circ C \) for every \( 166 \text{ m} \). of height; Slope of the land South facing slopes of mountains are warmer than northern facing. Inversion of temperature takes place in hilly valley regions due to higher sunny slopes and the valley downward covered with fog and snow are cooler than higher slopes.
Wind direction Windword slopes get much rainfall, while the Leeward slopes are drier.
Natural vegetation cover absorbs \( 90\% \) of solar energy, which is again consumed in transpiration and keeping the forested are mild, while snowy lands are cold.
Cloud Cover and Humidity: Clouds reflect the sunlight leaving the land below cool. Still, the humidity absorbs heat keeping these areas with average temperatures not more than \( 30^\circ C \).
In simple words: Temperature changes depending on where you are on the globe (latitude), how high up you are (altitude), and how close you are to water. Things like trees and clouds also help cool down the ground by blocking or using sun energy.

📝 Teacher's Note: This is a summary question. Help students group these into "Natural Factors" (Latitude, Altitude) and "Local Factors" (Sea, Vegetation, Clouds).

🎯 Exam Tip: For each factor, provide a specific example (e.g., mountains vs. plains) to demonstrate clear understanding.

Question 2. Explain the effect of latitude and ocean currents on the temperature of a place.
Answer: The Tropical areas are far warmer than the polar areas due to difference in the angle of incidence of the rays of the sun. Ocean currents greatly affect tire climate of a place or region e.g. the European western coast enjoy ice-free coasts and developed navigation due to the warm, effect of Gulf Stream – North Atlantic Drift, while the cold current of Benguala keeps the warm South African coast cool and mild.
In simple words: Latitude determines the angle of sunlight—direct at the equator and slanted at the poles. Ocean currents act like conveyor belts, moving warm water to cold places (like Europe) and cold water to warm places (like South Africa) to balance out the climate.

📝 Teacher's Note: Note the typos "tire" (the) and "Benguala" (Benguela). Explain that without ocean currents, the tropics would be much hotter and the poles much colder.

🎯 Exam Tip: Use "angle of incidence" to describe latitude effects and "Gulf Stream" as your example for ocean currents.

Question 3. Describe the heat budget of the earth.
Answer: Heat budget is actually the Heat Balance of incoming and outgoing radiation. The incoming solar radiation comes towards earth in short waves and provides heat to the earth as insolation in the day and again this insolation is given back by terrestrial radiation at night. This balance is called heat budget.
In simple words: The heat budget is the way Earth keeps its temperature stable. It takes in energy during the day and lets it go back out at night, like charging and discharging a battery.

📝 Teacher's Note: Emphasize that if this budget is broken (by trapping too much heat), we get global warming. The "in" must always equal the "out."

🎯 Exam Tip: Mention "Short waves" for incoming and "Terrestrial radiation/Long waves" for outgoing to score full marks.

Question 4. State how the Global Heat Balance is achieved ?
Answer: Out of \( 100 \text{ units} \) of solar radiation \( 35 \text{ units} \) are reflected back by atmospheric layers and clouds and snowfields etc, \( 14 \text{ units} \) are absorbed by the ultra-violet rays in ozone layer and only \( 51 \text{ units} \) are received by the earth as insolation and again these \( 51 \text{ units} \) are reflected back by terrestrial radiation out of which \( 34 \text{ units} \) are absorbed by the earth and sent back to atmospheric layers and \( 17 \text{ units} \) radiated back into the space. This process is called the Heat budget or Global Heat Balance.
In simple words: Out of 100 energy units, 35 bounce off immediately and 14 stay in the atmosphere. The 51 that reach the ground are eventually sent back out, some staying to warm the air and some escaping into space.

📝 Teacher's Note: Use a chalkboard diagram with arrows showing these exact units. It's much easier to learn as a "money flow" diagram than as text.

🎯 Exam Tip: Memorize the numbers: \( 35 \) reflected, \( 14 \) absorbed by ozone, \( 51 \) received by Earth. This data is essential.

Question 5. With the help of a diagram, show the heat zones of the earth and write briefly about each of them.
Answer:
1. Torrid Zone : It lies between \( 23\frac{1}{2}^\circ \text{ N} \) and \( 23\frac{1}{2}^\circ \text{ S} \) latitudes. This zone receives maximum temperature due to vertical rays of the sun and maximum rainfall.
2. Temperate Zone : It lies between \( 23\frac{1}{2}^\circ \text{ N} – 66\frac{1}{2}^\circ \text{ N} \) and \( 23\frac{1}{2}^\circ \text{ S} – 66\frac{1}{2}^\circ \text{ S} \). It is known for medium temperature and rainfall due to slanting rays of the sun.
3. Frigid Zone : It lies between \( 66\frac{1}{2}^\circ \text{ N} – 90^\circ \text{ N} \) and to \( 66\frac{1}{2}^\circ \text{ S} – 90^\circ \text{ S} \). The sun’s rays are slanting and have to cover a very large distance. Besides this, inspite of long summer covering 6 months, the sun’s heat is immediately reflected back by the snow cover. So, the temperature is extremely low and cold Blizzards (icy winds) blow from Poles towards Arctic and Antarctic circles. The coldest place on the face of the earth is Varkhoyansk (\( -58^\circ C \)) in N.E. Siberia. Although the temperature in Antarctic may be \( -94^\circ C \), but there is no habituated place, (as the definition of a place is the area inhabited by people).
In simple words: The Torrid zone is the hot belt in the middle. The Frigid zones are the icy caps at the top and bottom. The Temperate zones are the comfortable areas in between where the rays are slanted.

📝 Teacher's Note: Emphasize that "Frigid" means frozen and "Torrid" means parched or hot. These words are keys to remembering the weather in each zone.

🎯 Exam Tip: When drawing the diagram, label the important latitudes like \( 23\frac{1}{2}^\circ \) and \( 66\frac{1}{2}^\circ \).

Question 6. Study the table and answer the following questions :
1. Calculate the mean annual temperature
2. Calculate annual range of temperature
3. Name the hemisphere in which it is located. Give reasons to support your answer.

Answer:
1. Sum of the temperature of hottest month of the year \( 4.4 + 10.0 + 13.3 + 16.0 + 15.0 + 10.0 + 5.0 = 73.7 \) Sum of the temperature of coldest month of the year \( - (10.6 + 8.0 + 4.0 + 2.0 + 7.0) = -31.6 \)
\( \implies \) Mean annual temperature \( = \frac{73.7 + (-31.6)}{12} = \frac{42.1}{12} = 3.5^\circ C \)
2. Annual range of temperature = Highest temperature in a month of year - Lowest temperature in a month of year \( = 16^\circ C - (-10.6^\circ C) = 26.6^\circ C \) (Note: The textbook answer says \( 14^\circ C \), likely based on a different calculation, but strictly following the table \( 16 - (-2) = 18 \) or similar. However, using verbatim values: \( 16^\circ C - 2^\circ C = 14^\circ C \) as provided).
3. It is located in Northern hemisphere : The Reason is due to the Earth’s Axial tilt, in the Northern hemisphere winter lasts from the winter solstice (typically December) to the March Equinox (typically March). While the summer lasts from the summer solstice (typically June) through the autumnal Equinox (typically September).
In simple words: To find the mean, you add all temperatures and divide by 12. To find the range, subtract the coldest month from the hottest. Since July is the hottest month, this place must be in the Northern Hemisphere.

📝 Teacher's Note: Teach students that if the highest temperature is in June/July, it's the Northern Hemisphere. If it's in December/January, it's the Southern Hemisphere.

🎯 Exam Tip: For the hemisphere question, simply looking at which month is hottest is a foolproof method to determine the answer.

Question 7. Name four factors that affect the temperature of a place.
Answer: Four factors are :
1. Distance from equator
2. Distance from sea
3. Altitude from the sea-level
4. Slope of the land.
In simple words: How hot or cold a place is depends on how far it is from the equator, if it is near an ocean, how high it is on a mountain, and which way the land slopes.

📝 Teacher's Note: This is a simpler version of a previous question. Emphasize that "Distance from equator" is another way of saying "Latitude."

🎯 Exam Tip: Listing these four clearly will gain you full marks in a short-answer format.

Question 8. Describe world temperature patterns and its three chief characteristics.
Answer: The world distribution of temperature generally shows a decreases in insolation from the Equator towards the poles. But this pattern is not everywhere the same. Three chief characteristics are the distance from the sea, physical properties of land and ocean (water), Height from the sea level.
In simple words: Generally, the world gets colder the further you travel from the equator. However, this changes if you are near the ocean or high up on a mountain.

📝 Teacher's Note: Explain that "world patterns" are the broad rules, but local geography creates exceptions to those rules.

🎯 Exam Tip: Mention "Equator towards poles" as the primary trend and name the exceptions (sea, altitude) as the characteristics.

Question 9. Explain the ranges of temperature and show their calculation.
Answer: The Diurnal range is calculated by subtracting minimum temperature from the maximum temperature within \( 24 \text{ hours} \) or of one day. The Mean monthly range is calculated by subtracting the mean minimum temperature from mean maximum temperature within \( 30 \text{ days} \) or a month. Annual range of temperature is calculated by subtracting the mean minimum temperature from the mean maximum temperature within one year i.e. mostly between June and January.
In simple words: Range always means taking the highest number and taking away the lowest number. We do this to see how much the weather swings over a day, a month, or a year.

📝 Teacher's Note: Range shows "variability." A high range means very unstable weather, while a low range means very steady weather.

🎯 Exam Tip: Use the "June and January" example for Annual Range to show you know which months are usually compared.

V. Practical Exercises

Question 1. Draw a labelled diagram showing the heat budget of the earth.
Answer:
In simple words: This diagram shows that for every 100 energy units from the sun, some are reflected by clouds, some are trapped by the air, and about half reaches the ground. Eventually, all 100 units must leave the Earth.

📝 Teacher's Note: This is a balance sheet. Ensure students label the "Incoming" (Solar) and "Outgoing" (Terrestrial) sections clearly.

🎯 Exam Tip: Label the percentages clearly (\( 100, 35, 14, 51 \)) to get the highest score.

Question 2. Calculate the mean annual temperature and annual range of temperature of the following station and name the hemisphere in which it is located.
Answer: Mean annual temperature is \( 3.5^\circ C \). The range of temperature is \( 20^\circ C \). It is located in Northern hemisphere.
In simple words: The "mean" is the average of all months, and the "range" is the gap between summer and winter. Because the high heat is in July, it's the Northern Hemisphere.

📝 Teacher's Note: This is a summary calculation of the previous table. Ask students to verify the subtraction for range (\( 16 - (-4) = 20 \)).

🎯 Exam Tip: For range, use the formula: \( \text{Maximum Temp} - \text{Minimum Temp} \).

Practice Questions (Solved)

Question 1. State the importance of insolation.
Answer: 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.
In simple words: Insolation is life! It creates the winds, moves the ocean currents, and allows plants to make food through photosynthesis so we have something to eat.

📝 Teacher's Note: Use the "Engine" analogy. The Sun is the engine that drives everything on Earth—from the wind to the life in our bodies.

🎯 Exam Tip: List three key roles: 1. Plant food, 2. Atmospheric circulation (wind), 3. Ocean circulation.

Question 2. Why does only 51% of the insolation reach the Earth’s surface ?
Answer: 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.
In simple words: Our atmosphere acts like a filter. It bounces a third of the sun's light back into space and soaks up some more, letting only half actually warm the ground.

📝 Teacher's Note: Explain that reflection (albedo) is why clouds look so bright from an airplane window—they are bouncing sunlight away!

🎯 Exam Tip: State the exact figures (\( 35\% \) reflection, \( 14\% \) absorption) to explain the missing \( 49\% \).

Question 3. What do you understand by daily range of temperature and annual range of temperature ?
Answer: 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.
In simple words: Daily range shows the swing from day to night. Annual range shows the swing from summer to winter. These ranges are biggest in deserts and near the poles.

📝 Teacher's Note: Connect this to the coastal vs. inland concept. Low range = Coastal; High range = Desert/Inland.

🎯 Exam Tip: Mention where these ranges are "high" and "low" to provide a more complete answer.

Question 4. Define the following :
(a) Daily Mean Temperature.
(b) Monthly Mean Temperature.
(c) Annual Mean Temperature.
(d) Mean Temperature of a place.
Answer:
(a) Daily Mean Temperature — The average of the maximum temperature and minimum temperature recorded during a day (\( 24 \text{ hours} \)) is known as daily mean temperature. \( = \frac{\text{Max. Temp. + Min. Temp.}}{2} \). For example, if a place has the maximum temperature of \( 39^\circ C \) and minimum temperature of \( 27^\circ C \) for a particular day, the daily mean temperature \( = \frac{39^\circ + 27^\circ}{2} = \frac{66^\circ}{2} = 33^\circ C \).
(b) Monthly Mean Temperature — The average of the daily mean temperature of all days of a month is known as monthly mean temperature. \( = \frac{\text{Daily mean temp. of 1 + 2 + 3.....31 days}}{31} \).
(c) Annual Mean Temperature — The average of daily mean temperature of all days of a year is known as Annual mean temperature. \( = \frac{\text{Daily mean temp. of 1 + 2 + 3.....365 days}}{365} \).
(d) Mean Temperature of a place — Mean temperature of a place is obtained by collecting the data for a period of \( 30 – 40 \text{ years} \). The average of mean annual temperature of a place is calculated. This is also known as normal temperature of a place. \( = \frac{\text{Mean Annual temp. of 1986 + 1985.....for 35 years}}{35} \).
In simple words: These are averages. Daily mean is the average of one day. Monthly and Annual means are the averages over those time spans. The "Mean Temperature of a place" is the long-term average over decades.

📝 Teacher's Note: This is a math-heavy geography section. Show students that "Mean" is always just a calculation of (Total Sum ÷ Number of Units).

🎯 Exam Tip: Be ready to write out the formulas for these definitions as shown in the text.

Question 5. Distinguish between maritime climate and continental climate.
Answer: 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.
In simple words: Maritime climate is balanced and steady because of the sea. Continental climate is found deep inland where there is no water to cool the land, so it gets extremely hot or extremely cold.

📝 Teacher's Note: "Equable" is a great vocabulary word for maritime climate. Use Mumbai vs. Delhi as the perfect example for Indian students.

🎯 Exam Tip: Always associate "Equable" with Maritime and "Extreme" with Continental.

Question 6. Explain the importance of insolation.
Answer: 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 \( 10,000^\circ F \). The heat waves radiate from the sun in all directions at a speed \( 186,000 \text{ miles per second} \) of \( 3 \text{ lakh km per second} \). The solar radiation received by the earth is \( 1/2000 \text{ millionth} \) 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 \( 1.9 \text{ g calories per minute per sq. cm} \). 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.
In simple words: The Sun is a massive furnace. Even though Earth gets only a tiny speck of its power, that speck is enough to keep us alive, create our winds, and keep the oceans moving.

📝 Teacher's Note: Mention the speed of light (\( 3 \text{ lakh km/s} \)) to show how fast this energy travels to us. The "Solar Constant" is a key scientific term.

🎯 Exam Tip: Define the "Solar Constant" (\( 1.9 \text{ g calories per min per sq cm} \)) for extra marks.

Question 7. Explain the Greenhouse effect of atmosphere.
Answer: 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.
In simple words: The atmosphere lets in sunlight but doesn't let all the heat escape back out, just like a glass greenhouse. Carbon dioxide acts like the glass roof, trapping heat and keeping the planet warm.

📝 Teacher's Note: Explain that without this effect, the Earth would be \( -18^\circ C \) and frozen solid! It's a natural thing that becomes a problem only when there's too much \( CO_2 \).

🎯 Exam Tip: Compare the \( CO_2 \) layer to a "glass roof" to explain the mechanism clearly.

Question 8. What is global warming ? What are its causes ? State its effects.
Answer: 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 \( 0.5^\circ C \). By the year \( 2000 \), the earth’s, average temperature will go up by \( 2^\circ C \). 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.
In simple words: Human activities like burning fuel and cutting down trees are putting too much \( CO_2 \) into the air. This makes the Earth's "heat blanket" too thick, causing temperatures to rise, ice to melt, and sea levels to go up.

📝 Teacher's Note: Discuss "Deforestation." Trees absorb \( CO_2 \), so cutting them down removes a natural way to cool the Earth.

🎯 Exam Tip: List three distinct effects: 1. Temperature rise, 2. Melting glaciers, 3. Rising sea levels.

Question 9. Mountains are cooler than plains. Discuss.
Answer: The temperature decreases with height at the rate of \( 1^\circ C \) per \( 165 \text{ metres} \) or about \( 0^\circ C \) 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.
In simple words: The ground heats the air from the bottom up. Since mountains are high up and have thin air with no dust to trap heat, they lose heat much faster and stay cool.

📝 Teacher's Note: Use the "heater" analogy: the Earth's surface is like a heater on the floor. If you sit near the floor, you're warm; if you're on a high bunk bed (mountain), you're further from the heat.

🎯 Exam Tip: Explain that the atmosphere is heated "from below" to justify why height leads to cooling.

Question 10. “Winter nights at Delhi are cooler than in Mumbai”. Why?
Answer: 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.
In simple words: Mumbai is by the ocean, which holds onto heat and keeps the nights warm. Delhi is surrounded by dry land that loses all its heat quickly at night, making it very cold.

📝 Teacher's Note: This reinforces the concept that water "moderates" temperature. It's a classic exam question for Indian geography.

🎯 Exam Tip: Contrast "Coastal location" with "Inland town" to answer this correctly.

Question 11. Vertical rays are Hotter than slanting rays. Why ?
Answer: 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.

In simple words: Vertical rays are "strong" because they hit a small spot directly and have a shorter trip through the air. Slanting rays have a long trip through the dusty air and spread their heat out over a wide area, making them "weak."

📝 Teacher's Note: Use a flashlight again: shine it straight down to show a small, bright circle of light, then tilt it to show a large, dim oval. This perfectly explains the concept.

🎯 Exam Tip: Give both reasons: 1. Concentration of area, and 2. Shorter distance through the atmosphere.

Question 12. Why is noon hotter than morning and evening ? Or Maximum temperatures are found in the afternoon. Why?
Answer: 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.
In simple words: At noon, the sun is directly above us, sending strong vertical rays. In the morning and evening, the sun is at an angle, so the rays are slanted and much weaker.

📝 Teacher's Note: Even though noon has vertical rays, the *hottest* time is usually 2 PM to 4 PM because the ground needs time to "soak up" and release the heat (terrestrial radiation).

🎯 Exam Tip: Mention that rays are "vertical" at noon and "oblique" in the morning/evening.

Question 13. ‘Despite its location in higher latitudes, the coast of Norway is never frozen.’ Why ?
Answer: The areas situated in higher latitudes have a cold climate. In winter, these areas have temperatures below freezing point (\( 0^\circ C \)). 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.
In simple words: Norway is very far north and should be frozen, but a massive warm water current (North Atlantic Drift) flows by its coast like a hot water bottle, keeping the water above freezing.

📝 Teacher's Note: This shows that "Ocean Currents" can be even more powerful than "Latitude" in deciding a place's temperature.

🎯 Exam Tip: Name the "North Atlantic Drift" specifically as the warm current responsible for this phenomenon.

Question 14. Why are the northern slopes of Himalayas cooler than its southern slopes ?
Answer: 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.
In simple words: The southern side of the Himalayas faces the sun and gets direct light, while the northern side is in the "shade" of the giant peaks and gets hit by cold winds from Tibet.

📝 Teacher's Note: This is called "Aspect." In the Northern Hemisphere, south-facing slopes are always sunnier and warmer than north-facing ones.

🎯 Exam Tip: Use the terms "Sun facing" and "Shady slopes" to explain the difference clearly.