Voyage Solutions for ICSE Class 9 Geography Chapter 2 Geographic Grid Latitudes And Longitudes

Geographic Grid: Latitudes And Longitudes

Exercises

I. Short Answer Questions

Question 1. What is a geographic grid?
Answer: The network of the latitudes and the longitudes is known as a geographical grid.
In simple words: Imagine drawing horizontal and vertical lines all over a ball to make a net; that net on Earth is the geographical grid used to find any location.

📝 Teacher's Note: Use a globe and some string to show how these lines cross each other to form a "net" or grid pattern.

🎯 Exam Tip: Remember that a grid is always a "network" of crossing lines; use this keyword to define it clearly.

Question 2. Who devised the lines of latitude and longitude?
Answer: Eratosthenes, the Greek philosopher, first time devised the lines of latitude and longitude.
In simple words: A Greek thinker named Eratosthenes was the first person to come up with the idea of using these lines to map the world.

📝 Teacher's Note: Mention that Eratosthenes was also famous for calculating the circumference of the Earth with surprising accuracy for his time.

🎯 Exam Tip: Scientific names and inventors are common one-mark questions; memorize the spelling "Eratosthenes."

Question 3. What are lines of latitude and longitude?
Answer: The latitudes are the parallel circles with respect to the equator reducing in length northwards and southwards and the poles are the points only. On the other hand longitudes are equal in length drawn from North Pole to South Pole with their intervals reducing towards poles.
In simple words: Latitudes are horizontal circles that get smaller as they move toward the poles. Longitudes are vertical semi-circles that go from top to bottom and are all the same length.

📝 Teacher's Note: Use the analogy of an orange: the slices are like longitudes, while the horizontal cuts are like latitudes.

🎯 Exam Tip: Highlight the difference in shape: latitudes are full circles (except the poles), while longitudes are semi-circles of equal length.

Question 4. Mention two characteristics of lines of latitude?
Answer:
(a) The lines of latitude are parallel to the equator.
(b) The lines of latitude are drawn at an angular distance with respect to the equator.
In simple words: Lines of latitude never touch each other (they are parallel) and they measure how far North or South you are from the middle of the Earth (the Equator).

📝 Teacher's Note: Emphasize that "parallel" means they stay the same distance apart, which is why latitudes are called "parallels."

🎯 Exam Tip: Always mention that latitudes are measured in degrees as an "angular distance" to get full marks.

Question 5. Name the two hemispheres of the earth made by the Equator.
Answer: Northern hemisphere and Southern hemisphere.
In simple words: The Equator acts like a belt that cuts the Earth into a top half (Northern) and a bottom half (Southern).

📝 Teacher's Note: "Hemi" means half and "sphere" is a ball shape, so it literally means "half-ball."

🎯 Exam Tip: Spelling is important here; ensure "hemisphere" is written correctly.

Question 6. Express \( 1^{\circ} \) angular distance in kilometres.
Answer: As the circumference or the equator is nearly about \( 40,000 \text{ km} \).
\( \implies \) So \( 1^{\circ} \) angular distance in km. will be \( 40,000 / 360 = 111 \text{ km} \) approximately.
In simple words: Because a full circle is \( 360^{\circ} \), dividing the Earth's total distance by 360 tells us that each degree is about \( 111 \text{ km} \) wide.

📝 Teacher's Note: Show the calculation on the board to help students understand that geography often involves simple math.

🎯 Exam Tip: Remember the value \( 111 \text{ km} \) as it is a standard unit used in many geographical calculations.

Question 7. Name the thermal zones of the earth.
Answer: The thermal zones of the earth are Tropical, Temperate and Polar zones.
In simple words: These are heat zones: Tropical is the hottest, Temperate is mild, and Polar is the coldest.

📝 Teacher's Note: You can use a flashlight on a globe to show how direct light makes the center (Tropical) hotter than the tilted edges (Polar).

🎯 Exam Tip: Sometimes "Torrid" is used instead of "Tropical" and "Frigid" instead of "Polar." Know both terms.

Question 8. With the help of degrees, name the important lines of latitude.
Answer:
(a) Tropic of Cancer — \( 23\frac{1}{2}^{\circ} \text{N} \)
(b) Tropic of Capricorn — \( 23\frac{1}{2}^{\circ} \text{S} \).
(c) Arctic Circle — \( 66\frac{1}{2}^{\circ} \text{N} \).
(d) Antarctic Circle — \( 66\frac{1}{2}^{\circ} \text{S} \)
(e) North Pole — \( 90^{\circ} \text{N} \)
(f) South Pole — \( 90^{\circ} \text{S} \)
In simple words: These are specific markers on the map that tell us where heat zones start and end, like the Tropics and the Arctic circles.

📝 Teacher's Note: Have students practice drawing these lines on a blank circle to visualize their relative positions.

🎯 Exam Tip: Do not forget to add the 'N' or 'S' after the degree value; it is essential for defining the position.

Question 9. Which temperature zone receives almost vertical rays of the sun and which zones receive slanting rays?
Answer: The Tropical zone gets vertical rays of the sun, while temperate and polar zones receive slanting rays of the sun.
In simple words: The Sun shines straight down on the middle part of the Earth (Tropical), but its light hits the top and bottom parts at an angle (slanting).

📝 Teacher's Note: Explain that vertical rays are concentrated and hotter, while slanting rays spread out and are cooler.

🎯 Exam Tip: Use the term "vertical rays" for the Tropical/Torrid zone to score full marks.

Question 10. Which line is known as the Prime Meridian? State its importance.
Answer: Greenwich Meridian is called the ‘Prime Meridian’ or the \( 0^{\circ} \) longitude. The time is calculated with respect to this Meridian. So it is the basic Meridian and time is written as G.M.T. (Greenwich Meridian Time). The earth takes 4 minutes for moving \( 1^{\circ} \) distance.
In simple words: The Prime Meridian is the starting line for longitude (\( 0^{\circ} \)) that passes through London. We use it to set the world's clocks.

📝 Teacher's Note: Explain the history of why Greenwich (London) was chosen as the starting point during the 1884 International Meridian Conference.

🎯 Exam Tip: The \( 4 \text{ minutes per degree} \) rule is a "magic number" for time calculation problems.

Question 11. How can the general climate of an area be described with the help of the lines of latitudes?
Answer: The temperature decreases northwards and southwards from the equator. The region within \( 23\frac{1}{2}^{\circ} \text{N} \) and \( 23\frac{1}{2}^{\circ} \text{S} \) will get tropical climate with ample temperature and rainfall. On the other hand the regions between \( 23\frac{1}{2}^{\circ} \text{N} – 66\frac{1}{2}^{\circ} \text{N} \) and \( 23\frac{1}{2}^{\circ} \text{S} – 66\frac{1}{2}^{\circ} \text{S} \) will get temperate climate, while the regions known as Arctic and Antarctic circles get very cold polar climate as Tundra region.
In simple words: The further you move away from the Equator toward the poles, the colder it gets. We can predict if a place is hot, mild, or freezing just by looking at its latitude.

📝 Teacher's Note: This is the basis of climatic zones. Latitudes are the primary factor affecting Earth's temperature distribution.

🎯 Exam Tip: Mention the specific degrees (like \( 23\frac{1}{2}^{\circ} \)) when describing the zones for a more professional answer.

Question 12. Which line of longitude is used to fix the World Standard Time? State its value in degrees.
Answer: Greenwich Meridian is used to fix the World Standard Time. Its value in degrees is \( 0^{\circ} \). This time is written as G.M.T.
In simple words: The world's "standard" clock is set based on the \( 0^{\circ} \) line that passes through Greenwich.

📝 Teacher's Note: GMT is now often referred to as UTC (Coordinated Universal Time) in modern contexts, but GMT is the standard term in geography textbooks.

🎯 Exam Tip: Always state both the name (Greenwich Meridian) and the value (\( 0^{\circ} \)).

Question 13. State the longitudinal value in degrees of Indian Standard Meridian.
Answer: Longitudinal value of Indian Standard Meridian is \( 82\frac{1}{2}^{\circ} \text{E} \). It passes midway through India nearly along the city of Allahabad.
In simple words: To keep one single time across all of India, we use the line at \( 82\frac{1}{2}^{\circ} \text{E} \), which passes through Mirzapur/Allahabad.

📝 Teacher's Note: Discuss why India needs a standard meridian—it's because there is nearly a 2-hour time difference between Gujarat and Arunachal Pradesh!

🎯 Exam Tip: Mentioning "Allahabad" (or Mirzapur) adds specific geographical detail that examiners love.

Question 14. What is meant by IDL? State its importance.
Answer: IDL means the International Date Line, which is along \( 180^{\circ} \text{E & W} \). The date or day changes while crossing this line i.e. while there is Monday in the Eastern Hemisphere i.e. \( 0^{\circ} – 180^{\circ}\text{E} \), there will be Sunday in the Western Hemisphere i. e. \( 0^{\circ} – 180^{\circ} \text{W} \).
In simple words: The IDL is like a magic line in the ocean. When you cross it, you literally jump forward or backward by one whole day on the calendar.

📝 Teacher's Note: Use a globe to show that \( 180^{\circ} \text{E} \) and \( 180^{\circ} \text{W} \) are actually the exact same line on the opposite side of the Prime Meridian.

🎯 Exam Tip: Explain clearly how the day "gains" or "loses" to show you understand the concept fully.

Question 15. What are the Great Circle Routes? State their importance.
Answer: The Great Circle Routes follow the great circles i. e. the perimeters of the earth, which cover the shortest distances between any two places in spite of the zigzag routes along the surface of earth. These circles are beneficial for following the shortest distances between any two places and help in saving the time. i. e. the shortest routes are covered in minimum time span.
In simple words: These are the shortest paths between two points on the curved surface of the Earth. Pilots use them to save fuel and time when flying between far-away cities.

📝 Teacher's Note: Use a string on a globe to show that the shortest path between two points on a sphere looks like a curve on a flat map.

🎯 Exam Tip: The keywords here are "shortest distance" and "saving time/fuel."

Question 16. What is a globe? State the importance of a globe.
Answer: A globe is a man-made spherical model of the earth. A globe is very useful model to display the actual shape of the earth with its tilted axis ; The rotation and revolution of the earth can be very clearly shown by it along with the continents and oceans.
In simple words: A globe is a mini version of the Earth that shows us exactly how our planet looks, including its tilt and where the land and water are.

📝 Teacher's Note: Contrast the globe with a flat map to show why the globe is a more accurate representation of shape and size.

🎯 Exam Tip: Mention the "tilted axis" as an important feature shown by the globe.

II. Give reasons for each of the following

Question 1. Lines of latitude carve out the heat zones of the earth.
Answer: The Temperature goes on decreasing from the equator towards the poles. So the latitudinal zones are the actual heat zones of the earth, namely tropical, temperate and polar zones.
In simple words: Because sunlight hits different latitudes at different angles, the temperature changes as you move up or down, creating distinct hot, mild, and cold belts.

📝 Teacher's Note: Help students link latitude numbers to specific temperatures (Low latitude = High heat; High latitude = Low heat).

🎯 Exam Tip: The main reason is the "angle of the sun's rays" changing with latitude.

Question 2. Lines of longitude are also called Meridians of longitude?
Answer: The word ‘meridian’ means related to noon or 12 p.m. As every longitude receives the noon time or 12 p.m. at different intervals where the sun’s rays are exactly vertical over a particular longitude. On a particular longitude the noon-time is the same from north to south ; so a longitude is also called a Meridians of longitude.
In simple words: 'Meridian' means noon. Every place on the same longitude line has its noon at the exact same moment, so these lines are linked to time.

📝 Teacher's Note: Use this to explain words like A.M. (Ante-Meridiem) and P.M. (Post-Meridiem).

🎯 Exam Tip: Focus on the concept that "noon time is the same" along the entire length of a longitude.

Question 3. Diametrically opposite lines of longitude and the Equator are called Great Circles.
Answer: Every longitude along with its opposite longitude makes a complete circle around the earth and another complete big circle is the equator; while the latitudes make smaller circles along with the poles to be only points. So the equator and the longitudinal lines around the earth are called the Great Circles.
In simple words: A Great Circle is the biggest possible circle you can draw around the Earth. The Equator and any pair of opposite longitudes do exactly that—they split the Earth into two equal halves.

📝 Teacher's Note: Show that while all longitudes (as pairs) are Great Circles, the Equator is the *only* latitude that is a Great Circle.

🎯 Exam Tip: Define a Great Circle as a circle that "bisects the sphere" into two equal hemispheres.

Question 4. The Greenwich time is called Greenwich Mean Time.
Answer: The time of any place or country is calculated according to the \( 0^{\circ} \) longitude or Greenwich meridian, the time change is of 4 minutes for every \( 1^{\circ} \) longitude. So it is called Greenwich Mean Time.
In simple words: Because the world agreed to use the time at Greenwich as the "average" or "mean" starting point for everyone's clocks.

📝 Teacher's Note: "Mean" refers to the average solar time at that specific meridian.

🎯 Exam Tip: Link the term to the \( 0^{\circ} \) longitude for clarity.

Question 5. IDL deviates and goes zig-zag near some Islands in the Pacific ocean.
Answer: IDL is not a straight line, but it deviates in order to classify some scattered Islands in a particular divisions of Hemispheres, so that the day and time can be calculated according to the line, as the natural position of the Islands is haphazard.
In simple words: If the line were perfectly straight, it might cut right through a group of islands. This would mean one side of the street is Monday and the other is Sunday! To avoid this confusion, the line zig-zags around them.

📝 Teacher's Note: Mention specific countries like Kiribati that have shifted the line to keep their whole country on the same calendar day.

🎯 Exam Tip: The reason for the zig-zag is "to avoid having different dates within the same island group."

Question 6. A globe is the most popular model of the earth.
Answer: As our earth is spherical in shape, so it can be best represented by a spherical model like a globe. A globe illustrates the position of continents and oceans, the tilted axis of the earth, its rotation, the sea and air routes etc. So a globe is a perfect model of the earth.
In simple words: Maps are flat, but the Earth is round. A globe is round too, so it doesn't stretch or distort the shapes of continents like a flat map does.

📝 Teacher's Note: Remind students that "all maps lie" because you cannot flatten a ball without tearing or stretching it, whereas a globe stays true.

🎯 Exam Tip: Mention "no distortion of shape and size" as a key advantage of the globe.

III. Long Answer Questions

Question 1. Describe the lines of latitude, their importance and use.
Answer: The face of the earth is divided into various parallel circles with respect to the equator on both sides at different angular distances. These lines are very important to decide the climate and temperature range of any place or region as the temperature goes on decreasing from the equator to polewards.
In simple words: Latitudes are horizontal parallel lines. They are vital because they tell us about the climate—the closer a latitude is to the Equator, the warmer the region usually is.

📝 Teacher's Note: Use this to introduce the concept of "Latitude of a place" as its angular distance from the center of the Earth.

🎯 Exam Tip: Focus on the relationship between latitude and "heat distribution" for this descriptive answer.

Question 2. With reference to the International Date Line, state the following:
(a) It is meaning and application.
(b) The important deviations it makes and reasons for the same.
(c) Give an example of how time lost or gained is computed with reference to this line.
Answer:
(a) The time and date changes as we cross the International Date Line i.e. the navigators or pilots have to loose one day while crossing westwards and gain one day while crossing eastwards i.e. When one travels from Tokyo to San Francisco on Monday, he will reach San Francisco on Sunday.
(b) The International Date Line is not a straight line but have some deviations in order to adjust with the pattern of the landforms and some islands to decide for the time and date of these places and regions.
(c) If we are moving from Hawaii Islands towards Shanghai on Tuesday, we will reach there on Wednesday or Thursday probably, but if we are going eastwards from Shangai to Hawaii islands on Tuesday. We may reach there either on Tuesday or Monday.
In simple words: The IDL marks where one day ends and another begins. It bends to keep island groups together. Traveling across it feels like time travel because you gain or lose a day!

📝 Teacher's Note: This is a complex topic. Use a "Time-Date" wheel or a simulation to show how crossing the \( 180^{\circ} \) meridian flips the calendar.

🎯 Exam Tip: Memorize the rule: "Westward cross = Add a day; Eastward cross = Subtract a day."

Question 3. Describe the lines of longitude and state their use in relation to distance and time.
Answer: A longitude is the angular distance of a place east or west of the Prime Meridian or \( 0^{\circ} \) longitude. The lines of longitude are the great semi-circles joining North pole and South pole and are equal in length. These are \( 0^{\circ} – 180^{\circ} \text{E} \) and \( 0^{\circ} – 180^{\circ} \text{W} \) longitudes or total \( 360^{\circ} \). As the earth takes 24 hours to make a complete rotation along its axis crossing \( 360^{\circ} \) lines of longitude, so earth takes nearly 4 minutes to move one degree (\( 1^{\circ} \)) longitude or \( 111 \text{ km} \) length or distance. There is difference of time of one hour between \( 15^{\circ} \) interval of longitudes. According to the clock-time, EGA stands for East-Gain-Add and WLS means West Lose Subtract. In other words for each \( 1^{\circ} \) longitude towards east 4 minutes are to be added and towards west for each \( 1^{\circ} \) longitude 4 minutes are to be subtracted.
In simple words: Longitudes are vertical lines used to calculate time. Every degree move means a 4-minute change. If you go East, time is later; if you go West, time is earlier.

📝 Teacher's Note: Introduce the acronyms EGA (East Gain Add) and WLS (West Lose Subtract) to help students solve time-math problems quickly.

🎯 Exam Tip: Be ready to use the formula: \( \text{Longitude difference} \times 4 \text{ minutes} = \text{Time difference} \).

Question 4. Make a detailed study of finding time with the help of longitudes. Give one practical example.
Answer: Indian Standard Time is based on \( 82\frac{1}{2}^{\circ} \text{E} \) longitude. So if the time in India is 12 noon, so it will be 6.30 A.M. in England or GMT. The time difference between \( 0^{\circ} \) and \( 82\frac{1}{2}^{\circ} \text{E} \) will be \( 82.5 \times 4 = 330 \text{ minutes} \) or \( 330 / 60 = 5\frac{1}{2} \text{ hours} \). So there is difference of \( 5\frac{1}{2} \text{ hours} \) between India and England, as England lies in the west, so the time will be \( 5\frac{1}{2} \text{ hours} \) less than India.
In simple words: India is ahead of London by \( 5\frac{1}{2} \text{ hours} \). We calculate this by multiplying our longitude distance (\( 82.5^{\circ} \)) by 4 minutes and converting it to hours.

📝 Teacher's Note: Use the world map to show that India is to the East of Greenwich, hence it sees the sun earlier.

🎯 Exam Tip: Practice converting minutes to hours (e.g., 330 min = 5 hours 30 min) to avoid calculation errors in exams.

IV. Problem Solving

A cricket match was to be held at Birmingham at 9 a.m. local time. The position of Birmingham is \( 5^{\circ} \text{W} \). Calculate the time the viewers have to tune their television in Sydney \( 151^{\circ} \text{E} \).

Question. Calculate the time in Sydney for the Birmingham match.
Answer:
The local time at Birmingham is 9 am.
The location of Birmingham is \( 5^{\circ} \text{W} \) of Prime Meridian.
The GMT would be 9:20 a.m. [\( 9.00 \text{ hrs} + (5^{\circ} \times 4 \text{ min}) = 9.00 \text{ hrs} + 20 \text{ min} = 9.20 \text{ a.m.} \)]
Sydney is located at \( 151^{\circ} \text{E} \) of Prime Meridian.
At any point of time Sydney would be \( 151 \times 4 = 604 \text{ min} = 10 \text{ hrs } 4 \text{ min} \) ahead of GMT (Sydney is to the East of the Prime Meridian so local time would be ahead of GMT)
When it is 9:20 a.m. GMT the local time at Sydney would be (\( 9:20 + 10:04 \)) \( 19:24 \text{ hrs} \) or \( 7:24 \text{ p.m.} \)
In order to watch the Birmingham match at Sydney the viewers would have to tune their televisions at 7:24 p.m. local time.
In simple words: Since Sydney is far to the East of Birmingham, its time is much later. We find the time at the Prime Meridian first, then add the time for Sydney's distance to get the evening time.

📝 Teacher's Note: This "two-step" method (converting to GMT first) is the safest way to avoid mistakes when places are in different hemispheres (E and W).

🎯 Exam Tip: Always state whether the place is East or West of the Prime Meridian before adding or subtracting time.

Question 1. An important programme was to be broadcast from Mumbai at 7.30 p.m. This was heard by some Indian sailors near Ivory Coast in West Africa at \( 20^{\circ} \text{W} \) longitude. What was the local time there?
Answer: According to the Indian Standard Time 7.30 p.m. based on \( 82\frac{1}{2}^{\circ} \text{E} \) Longitude was the time at Mumbai. The longitudinal difference between Mumbai and Ivory Coast at \( 20^{\circ} \text{W} \) is \( 82.5 + 20 = 102.5 \).
\( \implies \) So \( 102.5 \times 4 = 410.0 \text{ minutes} = 6 \text{ hours } 50 \text{ minutes} \).
\( \implies \) i.e. the time will be 6 hours 50 minutes less than 7.30 p.m.
\( \implies \) So the time will be 12.40 p.m.
In simple words: Ivory Coast is much further West than Mumbai, so their time is earlier. By calculating the total degree gap, we find they are nearly 7 hours behind Mumbai.

📝 Teacher's Note: Remind students to add longitudes when one is East and the other is West to find the total distance between them.

🎯 Exam Tip: When moving from East to West (Mumbai to Ivory Coast), you must subtract the time difference.

Question 2. What is the longitude of a place where the local time 1:15 p.m. when it is 4 a.m. at Chicago (\( 88^{\circ} \text{W} \))?
Answer: The time difference between the two places is 9 hours and 15 minutes or \( 540 + 15 = 555 \text{ minutes} \).
\( \implies \) So the longitudinal difference will be \( 555 / 4 = 138.75^{\circ} \text{ degrees} \).
\( \implies \) So the longitude of the required place will be \( 50^{\circ} 45' \text{ E} \) i.e. it will cover \( 88^{\circ} \) from west to \( 0^{\circ} \) and \( 50^{\circ} 45' \) east from \( 0^{\circ} \) or Greenwich line.
In simple words: First, we find the time difference (over 9 hours). We convert that to degrees. Since the new place is later in time, it must be to the East of Chicago.

📝 Teacher's Note: Teach students that \( 0.75 \text{ degrees} \) is the same as \( 45 \text{ minutes of arc} \) (\( 0.75 \times 60 = 45 \)).

🎯 Exam Tip: If the time is later, the place is to the East. If the time is earlier, the place is to the West.

Question 3. Calculate the time at Durban (longitude \( 30^{\circ} \text{E} \)) when the time is 7.00 a.m. at New York (\( 75^{\circ} \text{W} \)).
Answer: The longitudinal difference between Durban and New York is \( 30^{\circ} + 75^{\circ} = 105^{\circ} \).
\( \implies \) so the time will be \( 105 \times 4 = 420 \text{ minutes} \) ahead from New York.
\( \implies \) There is the difference of 420 minutes or 7 hours, or 2 p.m.
In simple words: Durban is East of New York. We add their longitudes to find they are \( 105^{\circ} \) apart, which equals 7 hours. Adding 7 hours to 7 a.m. gives us 2 p.m.

📝 Teacher's Note: This is a standard East-West calculation. Always draw a simple timeline with \( 0^{\circ} \) in the middle to help students visualize it.

🎯 Exam Tip: Clearly show the addition of longitudes (\( 30 + 75 \)) to show how you got the total gap.

Question 4. Calculate the longitude of a place where the local time is 6.00 a.m., when the time is 9.00 p.m. at New Delhi on longitude \( 77^{\circ} \text{E} \).
Answer: The time difference between the required place and New Delhi is \( 6 + 9 = 15 \text{ hours} \).
\( \implies \) so the time in minutes \( = 15 \times 60 = 900 \text{ minutes} \).
\( \implies \) So the longitudinal difference \( = 900 / 4 = 225^{\circ} \).
\( \implies \) So the place will be in the west \( 225^{\circ} – 77^{\circ} = 148^{\circ} \text{ W} \).
In simple words: The new place is 15 hours behind Delhi. 15 hours equals \( 225^{\circ} \). Since it's behind, we move West from Delhi's \( 77^{\circ} \text{E} \) line until we reach \( 148^{\circ} \text{W} \).

📝 Teacher's Note: Remind students that moving west from \( 77^{\circ} \text{E} \) means crossing the \( 0^{\circ} \) line, so you subtract the starting longitude from the total degree change.

🎯 Exam Tip: Note that "9.00 p.m." to "6.00 a.m." is a backward leap of 15 hours.

Question 5. Calculate the local time at Singapore (\( 104^{\circ} \text{E} \)) when it is 6.00 p.m. at Greenwich.
Answer: The longitudinal difference at Singapore and Greenwich is \( 104^{\circ} \).
\( \implies \) so the time difference is \( 104 \times 4 = 416 \text{ minutes} \) i.e. 6 hours 56 minutes.
\( \implies \) So the time at Singapore will be 12.56 a.m.
In simple words: Singapore is far to the East of Greenwich. We add nearly 7 hours to the evening time at Greenwich, which takes us into the next morning in Singapore.

📝 Teacher's Note: When adding time that crosses midnight, make sure students remember to change the day (P.M. to A.M. next day).

🎯 Exam Tip: "East is ahead" – so you must add the calculated time to Greenwich time.

Question 6. Calculate the location of a place where the local time is noon when it is 7.30 p.m. at Greenwich.
Answer: Time difference is \( 12 – 7.30 = 4.30 \) or 4 hours 30 minutes.
\( \implies = 240 + 30 = 270 \text{ minutes} \).
\( \implies \) So the longitudinal difference is \( 270 / 4 = 67.5^{\circ} \).
\( \implies \) So the longitude is \( 67.5^{\circ} \text{W} \) or \( 67\frac{1}{2}^{\circ} \text{ W} \).
In simple words: The place is 4.5 hours behind Greenwich (it is noon there, but already evening in Greenwich). Since it's behind, the place must be in the West.

📝 Teacher's Note: Explain that "noon" means 12:00, which is earlier in the day than 7:30 p.m.

🎯 Exam Tip: Convert "half a degree" to "30 minutes of arc" (\( 67^{\circ} 30' \)) if required by the question format.

Question 7. What is the time and day at Mumbai (\( 73^{\circ} \text{E} \)) when it is Sunday 10.30 p.m. at Shillong (\( 92^{\circ} \text{E} \))?
Answer: The longitudinal difference is \( 92^{\circ} – 73^{\circ} = 19^{\circ} \).
\( \implies \) So the time difference is \( 19 \times 4 = 76 \text{ minutes} \) or 1 hours 16 minutes.
\( \implies \) or the time at Mumbai is 9.14 p.m.
In simple words: Mumbai is to the West of Shillong, so its time is earlier. It's exactly 1 hour and 16 minutes behind Shillong.

📝 Teacher's Note: This is an example of local time differences within the same country. This is why India uses a single Standard Time (IST) instead of local times.

🎯 Exam Tip: Since Mumbai is West of Shillong, subtract the time from 10.30 p.m. to get 9.14 p.m.

Practice Questions (Solved)

Question 1. How many lines of latitude are there?
Answer: \( 180 + 1 = 181 \)
In simple words: There are 90 lines North, 90 lines South, plus the Equator in the middle.

📝 Teacher's Note: Students often forget to count the Equator as the extra "+1" line.

🎯 Exam Tip: Always write the full sum (\( 180+1 \)) to show you've counted the Equator.

Question 2. How many lines of longitude are there?
Answer: \( 360 – 1 = 359 \).
In simple words: There are 360 lines, but because the \( 0^{\circ} \) and \( 180^{\circ} \) lines are shared or unique, the count is slightly different.

📝 Teacher's Note: Usually, we say there are 360 meridians. Some count them as 180 East and 180 West, but \( 0^{\circ} \) and \( 180^{\circ} \) are common lines.

🎯 Exam Tip: Most textbooks accept \( 360 \) as the general answer for "how many meridians."

Question 3. Which meridian is called Prime meridian?
Answer: \( 0^{\circ} \) meridian.
In simple words: It's the starting line for measuring East and West.

📝 Teacher's Note: Point it out on a map as the line that goes through London (Greenwich).

🎯 Exam Tip: "Prime" means first or primary, hence \( 0^{\circ} \).

Question 4. What is the latitude of equator?
Answer: \( 0^{\circ} \)
In simple words: The Equator is the very center, so it is the starting point for latitude.

📝 Teacher's Note: This is the baseline from which all other latitudes are measured.

🎯 Exam Tip: This is the most basic latitude value; memorize it.

Question 5. What is the latitude of Tropic of Cancer?
Answer: \( 23\frac{1}{2}^{\circ} \text{ North} \).
In simple words: It's the northern limit where the sun can shine directly overhead.

📝 Teacher's Note: Help students remember "Cancer" is North and "Capricorn" is South using alphabetical order (Cancer comes first).

🎯 Exam Tip: Do not forget to specify "North."

Question 6. What is the latitude of Tropic of Capricorn?
Answer: \( 23\frac{1}{2}^{\circ} \text{ South} \).
In simple words: It's the southern limit where the sun can shine directly overhead.

📝 Teacher's Note: This is the mirror image of the Tropic of Cancer in the Southern Hemisphere.

🎯 Exam Tip: Always write "South" after the degrees.

Question 7. Which is the longest line of latitude?
Answer: Equator.
In simple words: Since the Earth is fattest in the middle, the middle line is the biggest circle.

📝 Teacher's Note: This is why the Equator is called a "Great Circle."

🎯 Exam Tip: As you move away from the Equator, the lines of latitude get shorter.

Question 8. Which star is located vertically above the North pole?
Answer: Pole-Star
In simple words: Sailors used this star for centuries to find their way because it stays fixed over the North Pole.

📝 Teacher's Note: Also known as Polaris, it is a key celestial marker for navigation.

🎯 Exam Tip: This star helps in finding the latitude of a place in the Northern Hemisphere.

Question 9. Into how many time zones, has the world been divided?
Answer: 24
In simple words: One for each hour of the day.

📝 Teacher's Note: Each standard time zone is roughly \( 15^{\circ} \) of longitude wide (\( 360 / 24 = 15 \)).

🎯 Exam Tip: The world is divided into 24 standard time zones.

Question 10. What do you mean by meridians?
Answer: Lines of longitude.
In simple words: These are the vertical lines that connect the top and bottom of the Earth.

📝 Teacher's Note: Meridian is just another name for longitude, used especially when talking about time.

🎯 Exam Tip: "Meridian" and "Longitude" are interchangeable in most geography contexts.

Question 11. What is the relation between Temperature and Latitude of a place?
Answer: The temperature decreases with latitude.
In simple words: Higher latitude (further from Equator) means lower temperature (colder).

📝 Teacher's Note: This is because the Earth's curve causes sunlight to spread out more at higher latitudes.

🎯 Exam Tip: Use the phrase "inversely proportional" if you want to sound more advanced.

Question 12. What is latitude of North pole and South pole?
Answer: \( 90^{\circ} \text{ N} \) and \( 90^{\circ} \text{ S} \).
In simple words: These are the very top and very bottom points of the Earth.

📝 Teacher's Note: The poles are actually just points, not circles, because they are exactly \( 90^{\circ} \) from the Equator.

🎯 Exam Tip: \( 90^{\circ} \) is the maximum possible latitude.

Question 13. Why are there 180 parallels of latitude?
Answer: Because North pole to South pole (a hemisphere) has an angle of \( 180^{\circ} \).
In simple words: From top to bottom, the Earth covers a half-circle, which is \( 180 \text{ degrees} \).

📝 Teacher's Note: We count 90 degrees going up and 90 degrees going down from the middle line.

🎯 Exam Tip: The total number of parallels is actually 181 if you count the Equator (\( 90 \text{ North} + 90 \text{ South} + 1 \)).

Question 14. Name the two hemispheres of the Earth made by the equator?
Answer: Northern Hemisphere and Southern Hemisphere.
In simple words: The top half and the bottom half.

📝 Teacher's Note: Most of the world's land is in the Northern Hemisphere.

🎯 Exam Tip: This is a standard question about the Equator's main job.

Question 15. Which temperature zone receives slanting rays?
Answer: Polar Zone.
In simple words: The sun's light hits the poles at a very low angle, which is why it stays so cold there.

📝 Teacher's Note: Temperate zones also receive slanting rays, but they are most extreme at the Polar zones.

🎯 Exam Tip: Slanting rays spread out more and have less heat, which defines the Polar/Frigid zone.

Question 16. Name the two reference lines with respect to which the distances of various places on the earth’s surface are measured?
Answer: Prime Meridian and Equator.
In simple words: These are the "Starting Lines" for mapping—the Equator for Up/Down and Prime Meridian for Left/Right.

📝 Teacher's Note: These are the \( (0,0) \) coordinate points of our global mapping system.

🎯 Exam Tip: These are the "zero lines" of the geographic grid.

Question 17. What is the rate of change of time per degree of longitude?
Answer: 4 minutes per degree.
In simple words: Every time you move one degree of longitude, the time changes by 4 minutes.

📝 Teacher's Note: Help students derive this: \( 24 \text{ hours} \times 60 \text{ mins} / 360 \text{ degrees} = 4 \text{ mins/degree} \).

🎯 Exam Tip: This is the most important number to remember for time calculation problems.

Question 18. Why are the letters N or S added to latitude values?
Answer: The latitudes in Northern Hemisphere are marked N while the latitude in Southern Hemisphere marked S.
In simple words: Just saying \( 20^{\circ} \) doesn't help—we need to know if you are \( 20^{\circ} \) above the Equator (N) or below it (S).

📝 Teacher's Note: This is like giving an address; you need to specify the direction to find the house.

🎯 Exam Tip: Leaving out 'N' or 'S' makes a coordinate incomplete and technically wrong.

Question 19. Why are letters E or W added to longitude values?
Answer: The longitudes in the Eastern Hemisphere are marked E while the longitudes in the Western Hemisphere are marked W.
In simple words: They tell us if a place is to the right (East) or left (West) of the Prime Meridian.

📝 Teacher's Note: E and W show direction from London (Greenwich).

🎯 Exam Tip: These letters help determine if time should be added (E) or subtracted (W).

Question 20. What is the importance of Tropic of Capricorn?
Answer: It marks the Southern limit of tropical zone.
In simple words: It is the furthest point South where the Sun can be directly overhead once a year (on Dec 22).

📝 Teacher's Note: Explain its relationship to the winter solstice in the Northern Hemisphere.

🎯 Exam Tip: It is located at \( 23\frac{1}{2}^{\circ} \text{ S} \).

Question 21. What is meant by “the Parallels of Latitude?
Answer: If you examine a globe or map, you will see two sets of lines drawn across it. One set of lines runs north and south of Equator and Parallel to it. These lines are called Parallels of a Latitude. The total number of such lines, if drawn at a distance of one degree, from one another is 180 : 90 North of the equator and 90 South of the equator.
In simple words: They are circles that run parallel to the Equator. They never meet, just like railway tracks.

📝 Teacher's Note: Use the word "Parallel" to explain why they are called this—they stay the same distance apart all the way around.

🎯 Exam Tip: Note that latitudes are full circles, unlike longitudes which are semi-circles.

Question 22.
(a) What do you mean by Longitude of a place? How is longitude of a place determined?
(b) What is the “Prime Meridian”?
(c) What is the difference between Prime Meridian and other meridians of longitude?
(d) Explain how latitudes and longitudes help to determine the position of a place on the globe?
(e) Explain how the longitude of a place affects the time.

OR
State the rate of change of time with longitude.
Answer:
(a) Longitude is the distance of a place east and west of the Prime Meridian along a parallel of latitude. This distance is measured in degrees. When we say that the Longitude of Delhi is \( 77^{\circ} \) East, we mean that Delhi lies East of the Prime Meridian and its distance from the Prime Meridian is \( 77^{\circ} \). The Longitude of a place can be determined by comparing its Local Time with Greenwich Time. Greenwich Time can be known either by radio or by means of a watch which keeps Greenwich Time. Captains of ships generally use a Chronometer for this purpose. A Chronometer is a time piece which keeps accurate time and which is not affected by change in temperature. Now suppose that when it is 2 p.m. at Greenwich, another place shows 5 p.m. The difference between the times of two places is 3 hours, that is 180 minutes. Thus the place is \( = 180 / 4 = 45^{\circ} \) away from the Prime Meridian and since its time is ahead of Greenwich. Its longitude will be \( 45^{\circ} \) East.
(b) The Prime (or First) Meridian is the meridian from which longitude is measured. It is numbered. \( 0^{\circ} \) longitude. It is the meridian which passes through Greenwich (near London). Thus the Prime Meridian is also called Greenwich line.
(c) Other meridians of longitude are the lines which join all places having the same angular distance, east or west, of the Prime Meridian.
(d) The intersection of latitude and longitude points out the exact position of a place on the earth’s surface. For example London is situated at \( 51^{\circ} 30' \text{N} \) (latitude) and \( 0.5 \text{ W} \) (longitude). With the help of these intersecting lines, it is convenient to locate the position of London on the map. Actually, latitude and longitude are both imaginary lines drawn on a map or a globe in order to locate the position of a place or a region on the earth’s surface.
(e) As the Earth rotates from west to east about its own axis, the zone of illumination moves slowly towards the west. This accounts for variation in the time of Sunrise and Sunset at different places on the Earth. The Earth takes 24 hours to complete one rotation. This means that 360 degrees of longitude are covered in a period of 24 hours. This gives rise to a time difference of [\( 24 \times 60/360 \)] or 4 minutes for \( 1^{\circ} \) of longitude. The time difference is to be added in case of places to the east of a point. In case of places to the west, the time difference is to be subtracted. It is possible to calculate the time at a given place A from the time recorded at B and the longitude difference between stations A and B.
In simple words: Longitude tells you how far East or West you are and helps you figure out the local time. Where a longitude and a latitude cross, that's your exact "X marks the spot" location on Earth.

📝 Teacher's Note: This is a comprehensive review of the chapter. Use the ship and chronometer story to show how important longitude was for exploration and safety at sea.

🎯 Exam Tip: The "intersection point" of latitude and longitude is the most critical concept for locating a place.

Question 23.
(a) What is “Greenwich Mean Time”?
(b) How far is it correct to say that local time is the Sun time?
(c) How can you say that the use of ‘Local Time’ is very inconvenient nowadays in practical life?
(d) Why do some countries have many time zones?

OR
What are ‘Time Zones’?
Answer:
(a) Greenwich Mean Time (GMT):- It is based on \( 0^{\circ} \) longitude of a place of this name near London. GMT is adopted uniformly by all countries to keep time. It forms the basis of fixing Time Zones.
(b) When the Sun reaches the highest point in the sky, while crossing the meridian of any place, it is mid-day or 12.00 noon at that place. If watches are adjusted according to this time, then it will be known as local time. But the highest position of the sun can be found only on a sunny day. Therefore it is correct to say that local time is the Sun-time.
(c) Use of Local time is very inconvenient now-a-days in practical life, because if we have to travel through many countries, it will be convenient to us to follow one particular standard time, according to which we can set our watches with respect to a particular country and its standard time with reference to Greenwich or Prime Meridian (\( 0^{\circ} \) Longitude) to bring about international uniformity. This is known as Greenwich Mean Time (GMT). The Indian Standard time is 5 hrs 30 minutes ahead of GMT.
(d) Large countries like Russia, Canada and the United States have vast longitudinal extent. They do not have a single Standard Time for the whole Country. They have many time zones, with each time zone covering about \( 15^{\circ} \) of longitude. The erstwhile Soviet Union had 11 times zones to cover \( 165^{\circ} \) of longitudinal extent. Canada and the United States have five time zones extending from the Atlantic coast of the Pacific coast. There is time difference of five hours between the two coasts.
In simple words: Local time is based on the Sun, but it's hard to use when traveling. Instead, we use Standard Time zones so everyone in a country (or region) follows the same clock. Big countries like Russia need many zones because they are so wide.

📝 Teacher's Note: Discuss why India, despite being quite wide, chooses to have only one time zone, and how this simplifies railway and airline schedules.

🎯 Exam Tip: Countries with "vast longitudinal extent" (like Russia) are the ones that require multiple time zones.

Question 24. Give reasons for the following :
(a) There are no latitudes higher than \( 90^{\circ} \text{N} \) and \( 90^{\circ} \text{S} \).
(b) The opposite meridians of longitude form a Great Circle.
(c) Local time is a theoretical reality, while Standard Time is a practical necessity.
(d) “The International Date Line is not a straight line coinciding with longitude 180 degrees.” Why?
(e) The distance between two consecutive meridian, is equal to about 111 kilometres only at the equator.
(f) When it is noon at Cairo (\( 30^{\circ} \text{E} \)), the local time in New York (\( 75^{\circ} \text{W} \)) is 5.00 a.m.
(g) All parallel other than equator are not Great Circles.
(h) A person, travelling from Mumbai to London, alters the time on his watch at several places.
Answer:
(a) The total circumference of a circle is \( 360^{\circ} \) and the distance between the Equator and the North Pole is one-fourth of the circumference i.e. \( 90^{\circ} \). So we have 90 latitudes towards north and 90 towards south, which are denoted as \( 90^{\circ} \text{ N} \) and \( 90^{\circ} \text{ S} \) respectively.
(b) The opposite meridians of longitude form a Great circle because by each of them the world is divided into two equal parts.
(c) Local time may differ from place to place. Therefore, it is only a theoretic reality. On the other hand, standard time is the same for a particular country. It is a practical necessity for the sake of uniformity of time.
(d) The International Date Line passes through the Pacific ocean where there are no land masses. It follows \( 180^{\circ} \) meridian for most of its distance. The date line is zig-zag in some places to avoid the confusion of time on the same island. It avoids some islands and deviates from \( 180^{\circ} \). In Northern Hemisphere, it bends to the West of \( 180^{\circ} \) while in the Southern Hemisphere it bends Eastwards.
(e) The circumference of the Earth is approximately 40,000 km. It covers ah angle of 360 degrees. The distance between two consecutive parallels of latitude is everywhere the same. This is because lines of latitude are parallel lines. Therefore one degree of latitude. \( = 40,000 / 360 = 111 \text{ km} \) (approximately.) On the other hand, the distance between two consecutive meridians of longitude is 111 km only at the equator and gradually decreases with distance from the equator. This is because the meridians of longitude converge at the two poles.
(f)

Longitude of Cairo \( = 30^{\circ} \text{ E} \)
Longitude of New York \( = 75^{\circ} \text{ W} \)
Difference in Longitude \( = 30^{\circ} + 75^{\circ} = 105^{\circ} \)
(Add because Cairo is in the East of Greenwich and New York is in the West of Greenwich).
\( \implies \) Difference in time \( = 105 \times 4 = 420 \text{ minutes} = 7 \text{ hours} \).
As New York is situated in the West of Greenwich, its local time will be behind that of Cairo. So we subtract.
Local time at Cairo \( = 12:00 \text{ hrs} \)
Subtract \( = 7 \text{ hrs} \)
Local time at New York \( = 5:00 \text{ a.m.} \)
(g) All parallels of latitude are circles of different sizes, and only the equator is the circle whose center is the center of the Earth, which makes it a Great Circle. All others are Small Circles.
(h) it is because of change in longitude at several places.
In simple words: These are logical reasons for how our map system works. For example, Cairo and New York have different times because they are far apart in longitude. The IDL zig-zags to help people on islands stay on the same day.

📝 Teacher's Note: Part (e) is very important—it explains why longitudes are like orange slices that meet at the top and bottom, while latitudes are like stacks of rings.

🎯 Exam Tip: For time problems like (f), always use a small diagram or table to show your calculation steps clearly.

Question 25. What do you mean by the Latitude of place?
Answer: Latitude is the distance of a place north or south of the equator along a meridian. This distance is measured in degree. When we say that the Latitude of Delhi is 28-j North, we mean that Delhi lies North of the equator and its distance from the equator is \( 28\frac{1}{2} \).
In simple words: It tells us how far up or down a place is from the Earth's middle belt.

📝 Teacher's Note: Use the degree symbol and direction (N/S) to show how a place's "vertical address" is written.

🎯 Exam Tip: Define it as an "angular distance" for the best score.

Question 26. How are Latitudes measured?
Answer: The latitude of a place is the angular distance of the point north or south of the equator measured in degrees. The equator is taken as \( 0^{\circ} \) latitude. Latitudes are measured from \( 0^{\circ} \) to \( 90^{\circ} \text{ N} \) and \( 0^{\circ} \) to \( 90^{\circ} \text{ S} \). The distance from the equator to \( 90^{\circ} \text{ N} \) covers a distance of 1/4 of the circumference of the Earth or 140,000 km. One degree of latitude is equivalent to the length of about 111 km or 69 miles.
In simple words: We start at the Equator (\( 0^{\circ} \)) and measure angles up to the North Pole (\( 90^{\circ} \)) or down to the South Pole (\( 90^{\circ} \)). Every degree move is about \( 111 \text{ km} \) on the ground.

📝 Teacher's Note: Show that \( 90^{\circ} \) is exactly a quarter of a full \( 360^{\circ} \) circle.

🎯 Exam Tip: Remember the value \( 111 \text{ km} \) per degree of latitude—it's constant everywhere on Earth.

Question 27. Explain why the lines of longitude are called meridians of longitude?
Answer: Lines of longitude are lines which join all places having the same angular distance east or west of the Prime Meridian. All lines of longitude are semicircles of equal length. Lines of longitude are also called Meridians because all places along a lines of longitude experience mid-day at the same time.
In simple words: 'Meridian' relates to noon. Since everyone on the same line has noon at the same time, the name fits perfectly!

📝 Teacher's Note: Use a globe to show how a line of longitude passes through many cities that all see the sun at its highest point simultaneously.

🎯 Exam Tip: The key keyword here is "mid-day at the same time."

Question 28. State two properties of lines of latitude.
Answer:
1. The length of the lines of latitudes decrease with distance from the equator.
2. All lines of latitude are circles parallel to the equator.
In simple words: They never touch each other and they get smaller as you get closer to the poles.

📝 Teacher's Note: Contrast this with longitudes, which are all the same length but *do* meet at the poles.

🎯 Exam Tip: These are the "parallels," so "never intersect" is their most important property.

Question 29. State two properties of lines of longitude.
Answer:
1. The distance between two consecutive longitude decreases gradually with distance from the equator.
2. All lines of longitude are semicircles of equal length.
In simple words: Longitude lines are like the sections of an orange—widest in the middle and meeting at the top and bottom.

📝 Teacher's Note: Show how longitudes converge at the North and South Poles.

🎯 Exam Tip: Mention that longitudes are "semicircles," not full circles like latitudes.

Question 30. Clearly distinguish Longitude from Lines of Longitude.
Answer: Longitude is the distance of a place from the Prime Meridian while lines of longitude are lines drawn on a map or globe showing the longitude of all the places at the distance from the Prime Meridian. These lines join the north and south poles and cut the Equator at right angles.
In simple words: Longitude is the "number" (like \( 40^{\circ} \)), while a Line of Longitude is the actual mark on the map representing that number.

📝 Teacher's Note: It's like the difference between a "temperature" and a "thermometer line"—one is the value, the other is how we show it.

🎯 Exam Tip: Longitude is an angular distance; a meridian is a line.

Question 31. What do you mean by “Meridians or Lines of Longitude”?
Answer: The other set of lines join the north and south poles and cuts the equator at right angles. These lines are called Lines of Longitude or Meridians. The total number of such lines, if drawn \( 1^{\circ} \) apart, is \( 360^{\circ} – 180^{\circ} \text{ East} \) and \( 180^{\circ} \text{ West} \) of the Prime Meridian. It should be noted that \( 180^{\circ} \text{ East} \) and \( 180^{\circ} \text{ West} \) in the same lines.
In simple words: They are vertical lines that go from pole to pole. There are 360 of them in total.

📝 Teacher's Note: Highlight that \( 180^{\circ} \text{E} \) and \( 180^{\circ} \text{W} \) is just one single line on the back of the globe.

🎯 Exam Tip: Mention that they cut the Equator at "right angles" (\( 90^{\circ} \)).

Question 32. What is the latitude of:
1. Equator
2. North Pole
3. South Pole
4. Tropic of Cancer
5. Tropic of Capricorn
6. Arctic Circle
7. Antarctic circle? Also give their characteristics.
Answer:
1. Latitude of Equator: The latitude of the equator is \( 0^{\circ} \). Here the days and nights are equal throughout the year and the rays of the sun fall exactly vertically at noon on March 21 and September 23.
2. Latitude of North Pole: The latitude of the North pole is \( 90^{\circ} \text{ North} \) because it is situated north of the Equator at a distance of a quarter of the circumference of the earth. Here days and nights are of six-months duration.
3. Latitude of South Pole: Latitude of the south pole is \( 90^{\circ} \text{ south} \), because it is situated South of Equator at a distance of a quarter of the circumference of the earth. Here the days and night are of six months duration.
4. The Latitude of the Tropic of Cancer is \( 23\frac{1}{2} \text{ North} \). Here the rays of the sun fall vertically at noon on June 21.
5. The Latitude of the Tropic of Capricorn is \( 23\frac{1}{2} \text{ South} \). Here the rays of the sun fall vertically at noon on December 22.
6. The Latitude of the Arctic Circle is \( 66\frac{1}{2} \text{ North} \). Here once the year (June 21) the day is of 24 hours duration and once in the year (December 22) the night is of 24 hours duration.
7. The Latitude of the Antarctic Circle is \( 66\frac{1}{2} \text{ South} \). Here once in the year (December 22nd) the day is of 24 hours duration and once in year (June 21) the night is of 24 hours duration.
In simple words: Each of these lines is a milestone on Earth. They tell us when days are longest, when the sun is directly overhead, and where the freezing "24-hour sun" regions begin.

📝 Teacher's Note: This is a very important question. Use a chart to link the specific dates (like June 21) to the latitudes.

🎯 Exam Tip: Knowing the specific dates (Solstices and Equinoxes) for each line is vital for full marks.

Question 33. What adjustment has to be made when ships cross the International Date Line?

OR
Explain why a day appears to be lost in sailing round the world from east to west and gained when travelling from west to east.
Answer: The earth rotates on its axis from west to east, hence places in the east have their sun rise earlier than places in the west. Now if a man travels round the world from east to west, for every degree of longitude covered; he will have to set back his watch by four minutes. Thus after covering \( 360^{\circ} \) when he returns to the place from where he started he will have to set back his watch \( 360 \times 4 / 60 = 24 \text{ hrs} \). Thus he will appear to have lost a day. When Francis Drake returned to England after circumnavigating the globe, he thought it was Saturday, where as actually it was Sunday. The reason was that he had traveled from east to west, and had under calculated a day. On the other hand if a man travels from west to east, for every degree of longitude covered he will put forward his watch by four minutes and for \( 360^{\circ} \) he will forward it 24 hrs. When he returns to the place from where he started he will appear to have gained a day. When Cap. Basil Hailed reached Manila after circumnavigating the globe, he thought it was Monday; where as actually it was Sunday. The reason was that he had traveled from west to east and had over calculated a day.
In simple words: When you travel around the world, you keep changing your watch. By the time you get back to your start point, those small changes add up to one whole day. To fix this, we jump a day when crossing the IDL.

📝 Teacher's Note: Tell the story of the Magellan expedition—they kept a careful log but were one day off when they returned! This proves the need for an IDL.

🎯 Exam Tip: Eastward = Gain a day; Westward = Lose a day.

Question 34. Define Equator. What is its main function?
Answer: Equator is the parallel of zero degree latitude. It is an imaginary circle round the Earth bisecting it into halves i.e. Northern Hemisphere and Southern Hemisphere. It serves as reference line for the location of different places on the earth.
In simple words: The Equator is the "Zero Line" that splits the Earth into Top and Bottom halves. It's the most important latitude.

📝 Teacher's Note: The Equator is the only latitude that is also a Great Circle.

🎯 Exam Tip: Mention both its value (\( 0^{\circ} \)) and its function (dividing the hemispheres).

Question 35. What will be local time at Delhi \( 77^{\circ} \text{ E} \) longitude when is 3 p.m. at Tokyo \( 139^{\circ} \text{E} \) longitude?
Answer:
Longitude of Delhi \( = 77^{\circ} \text{E} \)
Longitude of Tokyo \( = 139^{\circ} \text{E} \)
Difference per degree \( = 139^{\circ} - 77^{\circ} = 62^{\circ} \)
\( \implies \) Difference of time per degree \( = 4 \text{ minutes} \)
\( \implies \) Difference between the time of Delhi and Tokyo \( = 4 \times 62 = 248 \text{ minutes} = 4 \text{ hours } 8 \text{ minutes} \).
Since Delhi lies west of Tokyo we shall subtract 4 hours 8 minutes from Tokyo time.
Hence local time at Delhi is 10.52 a.m.
In simple words: Tokyo is much further East than Delhi, so it sees the morning sun first. Delhi's time is therefore over 4 hours behind Tokyo's.

📝 Teacher's Note: When both places are in the same hemisphere (both East), you subtract the longitudes to find the gap.

🎯 Exam Tip: Since you are moving "West" from Tokyo to Delhi, remember to subtract the time.

Question 36. What will be the local time at Madras \( 80^{\circ} \text{E} \)? When it is 9 P.M. at New York \( 74^{\circ} \text{ W} \)?
Answer:
Longitude of Madras \( = 80^{\circ} \text{ E} \)
Longitude of New York \( = 74^{\circ} \text{ W} \)
\( \implies \) Difference in Degrees \( = 80^{\circ} + 74^{\circ} = 154^{\circ} \)
\( \implies \) Difference in time per degree \( = 4 \text{ minutes} \)
\( \implies \) Difference between the times of two places \( = 4 \times 154 = 616 = 10 \text{ hour } 16 \text{ minutes} \).
Since Madras lies East of New York, we shall add 10 hours 16 minutes to the local time of New York.
The local time at Madras will therefore, be 7.16 A.M. next morning.
In simple words: Madras and New York are on opposite sides of the world. The time gap is over 10 hours. Because Madras is East, it's already tomorrow morning there when it's night in New York.

📝 Teacher's Note: When places are in different hemispheres (E and W), add their longitudes to find the total distance.

🎯 Exam Tip: Adding 10+ hours to 9 P.M. crosses midnight, so the day changes to "next morning."

Question 37. “The degree of longitude decreases in length poleward”. Why?
Answer: Equator is the longest parallel on the Earth. All other parallels become shorter polewards due to spherical shape of the Earth. So the meridians near the poles have a narrow space. One degree of longitude is the longest at the equator (111 km) at \( 45^{\circ} \) latitude it is 79 km, at \( 60^{\circ} \) latitude it is 55 km and at poles, it is zero km.
In simple words: Think of lines on a beach ball. They are far apart in the middle (equator) but all bunch up at the very top and bottom. This means the gap between them gets narrower as you go up or down.

📝 Teacher's Note: Use an orange or a ball to show how longitudes meet at the poles, making the distance between them shrink to zero.

🎯 Exam Tip: The main reason is the "spherical shape of the Earth" and the "convergence of meridians at the poles."

Question 38. What is the relation between longitude and time?

OR
“There is a difference of 4 minutes of time for one degree of longitude”. Why?
Answer: There is a close relation between longitude and time. The Earth makes one complete rotation of 360 degrees in 24 hours. It passes through 15 degrees is one hour or one degree in four minutes. Thus, there is a difference of 4 minutes of time for one degree of longitude. As the Earth moves from West to East, the places East of Greenwich gain time whereas the places West of Greenwich loose time.
In simple words: The Earth rotates a full circle (\( 360^{\circ} \)) in a day. When you do the math (\( 1440 \text{ minutes} / 360 \text{ degrees} \)), you find that each degree takes 4 minutes to pass under the Sun.

📝 Teacher's Note: This calculation is the heart of timekeeping. Every student should know how to divide 1440 by 360.

🎯 Exam Tip: Mention "360 degrees in 24 hours" to explain how the 4-minute rule was found.

Question 39. “Lines of latitude are called parallels of latitude” Why?
Answer: Lines of latitudes join the places of same latitude. These are circles drawn round the earth, parallel to the equator. Therefore, these are called parallels of latitude.
In simple words: Because these lines are all perfectly centered on the Equator and stay exactly the same distance from each other all the way around the Earth.

📝 Teacher's Note: Just like railway tracks are parallel and never meet, these lines encircle the Earth without ever touching.

🎯 Exam Tip: The main reason they are called "parallels" is because they are "parallel to the equator."

Question 40. A ship crossing international date line at mid-night on Wednesday Eastwards, find that it is mid-night Tuesday on American side. Why?
Answer: A ship crossing international date line from West to East gains a day. It repeats a day. A day is subtracted from the calendar. So when it is Wednesday mid-night on Asiatic side, it is Tuesday midnight on the American side.
In simple words: When you fly or sail East across the IDL, you jump back in time by 24 hours. You actually get to live the same day twice!

📝 Teacher's Note: It's helpful to remember "Eastward = Earlier" when crossing the Date Line specifically.

🎯 Exam Tip: "Gaining a day" means you get more time, which happens by repeating the previous day's date.

Question 41. Mid-days Sun can be seen overhead in Chennai twice a year, but not even once in Delhi. Why?
Answer: Tropic of Cancer is the Northernmost limit of overhead Sun. Sun’s rays do not fall vertical beyond \( 23\frac{1}{2}^{\circ} \text{ N} \) latitude. Delhi is located North of Tropic of Cancer, so the Sun is never overhead at Delhi. But Chennai has overhead Sun twice a year.
1. When the Sun moves northward, from equator to Tropic of Cancer, the Sun is overhead at Chennai.
2. When the Sun shifts from Tropic of Cancer to equator, then again Chennai has overhead Sun.
In simple words: The Sun only shines perfectly straight down between the two Tropics. Chennai is inside this hot belt, but Delhi is too far North, outside the Sun's "straight down" zone.

📝 Teacher's Note: Chennai is at about \( 13^{\circ} \text{N} \) (inside the Tropics), while Delhi is at \( 28^{\circ} \text{N} \) (outside the Tropics). Use a diagram to show the Sun's limits.

🎯 Exam Tip: The key reason is Delhi's location "North of the Tropic of Cancer."

Question 42. Explain why there is no higher latitude other than \( 90^{\circ} \text{ N} \) and \( 90^{\circ} \text{ S} \).
Answer: Latitude is the angular distance from the plane of the equator. All of surfaces (planes) or circles make a maximum angle of \( 90^{\circ} \) from the plane of the equator. Therefore, maximum latitude is \( 90^{\circ} \text{ N} \) in the Northern Hemisphere and \( 90^{\circ} \) Southern Hemisphere.
In simple words: You can't go higher than "straight up" or lower than "straight down" from the center. A \( 90\text{-degree} \) angle is a perfect vertical corner, which is the maximum possible.

📝 Teacher's Note: The angle from the Equator to the center to the Pole is exactly a right angle (\( 90^{\circ} \)). You cannot go further than the pole itself.

🎯 Exam Tip: \( 90^{\circ} \) is the ultimate point of the Earth's axis.

Question 43. Name the five important parallels of latitude.
Answer:
(a) Equator is the starting line for all the parallels. It is zero degree parallel.
(b) Tropic of Cancer – \( 23\frac{1}{2}^{\circ} \text{ North} \) parallel.
(c) Tropic of Capricorn – \( 23\frac{1}{2}^{\circ} \text{ South} \) parallel.
(d) Arctic circle – \( 66\frac{1}{2}^{\circ} \text{ North} \) parallel.
(e) Antarctic circle – \( 66\frac{1}{2}^{\circ} \text{ South} \) parallel.
In simple words: These are the "VIP lines" on the globe that define our heat zones and seasons.

📝 Teacher's Note: These lines are chosen because of the way the Earth tilts as it orbits the Sun.

🎯 Exam Tip: Memorize both the name and the exact degree (with N/S) for all five.

Question 44.
(a) What do you mean by local time?
(b) What is the local time when it is noon at a place?
(c) What are the main characteristics of local time?
Answer:
(a) Local time : The local time of a place is the time of its own meridian. The local time is calculated by the position of the Sun at noon at a given place. When the Sun at any place is highest in the sky. It is noon.
(b) It is 12 o’clock. All the watches of that place should be set according to that time.
(c) Characteristics :
1. Every meridian has a different local time.
2. The places on the same meridian have the same local time.
3. The Eastern places will be ahead of Western places for local time.
4. Sundial was a simple and old method to determine local time.
In simple words: Local time is based on exactly when the sun is directly above you. When the sun is at its highest point, your local clock says it's exactly 12:00 noon.

📝 Teacher's Note: Use the sundial as a practical example. As the Earth rotates, every single longitude has its "noon" at a slightly different time.

🎯 Exam Tip: Remember that "East is Ahead" in local time because the sun rises in the East.

Question 45.
(a) What is the rule of changing the date while crossing the international date line?
(b) What is meant by ‘six-day week’ and ‘eight-day week’?
(c) Explain the above with the help of a map.
Answer: Rule : On crossing the date line, the ships adjust the dates according to the following rules :
(a) When crossing westward, towards Asia (from U.S.A. to Japan), a day must be added. When crossing the date line, ship misses a day from the calendar and have ‘six day week’. If a ship crosses the date line on Monday, the next day will be Wednesday and not Tuesday.
(b) When crossing eastward towards America (from Japan to U.S.A.) a day must be subtracted. When crossing the date line ships gain a day from the calendar and have an ‘eight- day week’. It repeats a day. If ship crosses the date line on Monday, the next day will be again Monday and not Tuesday.
In simple words: Going West? Skip a day (like losing Monday). Going East? Repeat a day (like having Monday twice). This keeps our world's calendar in sync.

📝 Teacher's Note: This is why the IDL is so fascinating. It prevents the confusion of different dates in a global world.

🎯 Exam Tip: West to East = Repeat day (gain time); East to West = Skip day (lose time).