Class 11 Geography Notes Chapter 3 (Latitude; Longitude and Time) – Practical Work in Geography Book
Alright class, let's delve into Chapter 3: Latitude, Longitude, and Time from your Practical Work in Geography book. This chapter is fundamental not just for your Class 11 understanding but also forms the bedrock for many questions in competitive government exams. Pay close attention to the concepts and definitions.
Chapter 3: Latitude, Longitude and Time - Detailed Notes for Exam Preparation
1. Introduction: The Geographic Grid
- To locate any place on the Earth's surface accurately, we use a system of imaginary lines drawn on globes and maps. This network of lines is called the Geographic Grid or Coordinate System.
- It consists of Parallels of Latitude and Meridians of Longitude.
- These lines intersect each other at right angles (90°).
2. Latitude
- Definition: Latitude is the angular distance of a point on the Earth's surface, measured in degrees, north or south of the Equator (0°).
- Measurement: It is measured from the centre of the Earth.
- Parallels of Latitude:
- These are imaginary circles running parallel to the Equator towards the North and South Poles.
- They run in an East-West direction.
- Key Parallels of Latitude:
- Equator (0°): The largest parallel, dividing the Earth into the Northern Hemisphere and the Southern Hemisphere. It is also a Great Circle.
- Tropic of Cancer (23½° N): Located in the Northern Hemisphere. The northernmost latitude at which the sun can be directly overhead.
- Tropic of Capricorn (23½° S): Located in the Southern Hemisphere. The southernmost latitude at which the sun can be directly overhead.
- Arctic Circle (66½° N): Marks the boundary of the North Frigid Zone. Experiences 24 hours of daylight/darkness on solstices.
- Antarctic Circle (66½° S): Marks the boundary of the South Frigid Zone. Experiences 24 hours of daylight/darkness on solstices.
- North Pole (90° N): The northernmost point on Earth.
- South Pole (90° S): The southernmost point on Earth.
- Characteristics of Parallels:
- All parallels are full circles, except for the North Pole and South Pole, which are points.
- The length of parallels decreases as we move away from the Equator towards the poles.
- All parallels are located at an equal distance from each other. (The distance between two consecutive degrees of latitude is approximately 111 km).
- Parallels are parallel to each other and never meet.
- Importance: Latitudes help determine the climate zones (Torrid, Temperate, Frigid) of the Earth based on the amount of solar insolation received.
3. Longitude
- Definition: Longitude is the angular distance of a point on the Earth's surface, measured in degrees, east or west of the Prime Meridian (0°).
- Measurement: Measured along the parallel of latitude passing through that point.
- Meridians of Longitude:
- These are imaginary semi-circles running from the North Pole to the South Pole.
- They run in a North-South direction.
- Key Meridians of Longitude:
- Prime Meridian (0°): The reference meridian passing through the Royal Observatory at Greenwich, near London. It divides the Earth into the Eastern Hemisphere and the Western Hemisphere.
- 180° Meridian: Located directly opposite the Prime Meridian. It roughly forms the basis for the International Date Line (IDL).
- Characteristics of Meridians:
- All meridians are semi-circles of the same length.
- They converge at the North and South Poles.
- The distance between meridians is maximum at the Equator and decreases towards the poles, becoming zero at the poles.
- Meridians intersect the Equator and all parallels of latitude at right angles (90°).
- Importance: Longitudes are primarily used to determine local time and standard time across the globe.
4. Longitude and Time
- Earth's Rotation: The Earth rotates on its axis from West to East. It completes one full rotation (360°) in approximately 24 hours.
- Relationship:
- 360° of longitude are covered in 24 hours.
- Therefore, 15° of longitude are covered in 1 hour (360/24 = 15).
- Or, 1° of longitude is covered in 4 minutes (60 minutes / 15° = 4 minutes).
- Time Calculation:
- Places east of a given longitude are ahead in time. (Gain time - Add)
- Places west of a given longitude are behind in time. (Lose time - Subtract)
- For every 1° longitude eastward, add 4 minutes.
- For every 1° longitude westward, subtract 4 minutes.
- Local Time: The time calculated based on the overhead position of the sun at a specific meridian. All places on the same meridian have the same local time (noon when the sun is highest).
- Standard Time:
- Countries with large east-west extent experience significant differences in local time across their territory. To avoid confusion, a country usually adopts the local time of a central meridian as the standard time for the entire country.
- This central meridian is usually a multiple of 7.5° or 15° longitude.
- Indian Standard Time (IST): Based on the local time of the meridian 82°30' E (82.5° E), which passes near Mirzapur (Uttar Pradesh).
- IST is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT) or Coordinated Universal Time (UTC). (Calculation: 82.5° * 4 minutes/° = 330 minutes; 330 minutes / 60 minutes/hour = 5.5 hours).
- Time Zones: The world is divided into 24 standard time zones, each ideally spanning 15° of longitude (though boundaries often follow political borders).
- Greenwich Mean Time (GMT) / Coordinated Universal Time (UTC): The time at the Prime Meridian (0° longitude) is the basis for calculating time worldwide.
5. International Date Line (IDL)
- An imaginary line, roughly following the 180° meridian, where the date changes by exactly one day when crossed.
- It runs through the middle of the Pacific Ocean, deviating around island groups (like Kiribati, Fiji, Tonga) to avoid splitting countries into different dates.
- Crossing the IDL:
- Travelling Eastward (e.g., from Asia to America): Subtract a day (Gain a day).
- Travelling Westward (e.g., from America to Asia): Add a day (Lose a day).
- It is not a straight line due to political and administrative convenience.
6. Great Circles and Small Circles
- Great Circle: Any circle drawn on the surface of a sphere whose plane passes through the centre of the sphere. It divides the sphere into two equal halves (hemispheres).
- Examples: The Equator and all Meridians of Longitude.
- Importance: The shortest distance between any two points on the Earth's surface lies along the arc of a Great Circle. This is crucial for navigation (air and sea routes).
- Small Circle: Any circle drawn on the surface of a sphere whose plane does not pass through the centre of the sphere.
- Examples: All Parallels of Latitude except the Equator.
7. Locating Places
- The intersection point of a specific parallel of latitude and a specific meridian of longitude gives the exact location of a place on the Earth's surface. Example: New Delhi is approximately 28° N Latitude and 77° E Longitude.
Key Takeaways for Exams:
- Memorize definitions of Latitude, Longitude, Equator, Prime Meridian, IDL.
- Understand the characteristics and differences between Parallels and Meridians.
- Know the key latitudes (Tropics, Circles, Poles) and their degree values.
- Master the calculation of time based on longitude (15° = 1 hour, 1° = 4 minutes; East=Gain/Add, West=Lose/Subtract).
- Know the Standard Meridian of India (82°30' E) and its time difference from GMT/UTC (+5:30 hours).
- Understand the concept of Great Circles and their significance for distance.
- Remember the direction of Earth's rotation (West to East).
- Understand why the IDL is necessary and why it deviates from the 180° meridian.
Multiple Choice Questions (MCQs)
Here are 10 MCQs based on the chapter for your practice:
-
Which of the following represents the angular distance of a place north or south of the Equator?
a) Longitude
b) Altitude
c) Latitude
d) Meridian -
The Prime Meridian passes through which city?
a) Paris
b) New York
c) Greenwich
d) Moscow -
What is the approximate distance between two consecutive parallels of latitude?
a) 101 km
b) 111 km
c) 121 km
d) 131 km -
If it is 12:00 Noon GMT (at 0° longitude), what would be the local time at 60° E longitude?
a) 8:00 AM
b) 4:00 PM
c) 6:00 PM
d) 10:00 AM -
Which of the following is a Great Circle?
a) Tropic of Cancer
b) Arctic Circle
c) Equator
d) Tropic of Capricorn -
Indian Standard Time (IST) is based on the local time of which meridian?
a) 75° E
b) 90° E
c) 82°30' W
d) 82°30' E -
What happens to the length of the parallels of latitude as one moves from the Equator towards the poles?
a) It increases
b) It decreases
c) It remains the same
d) It first increases then decreases -
A person travelling westward across the International Date Line will:
a) Gain a day
b) Lose a day
c) Experience no change in date
d) Experience shorter daylight hours -
The Earth rotates 1 degree of longitude in approximately how many minutes?
a) 1 minute
b) 4 minutes
c) 15 minutes
d) 60 minutes -
All meridians of longitude converge at:
a) The Equator
b) The Tropics
c) The Prime Meridian
d) The North and South Poles
Answer Key for MCQs:
- c) Latitude
- c) Greenwich
- b) 111 km
- b) 4:00 PM (Calculation: 60° E is east of GMT. Time difference = 60° * 4 min/° = 240 minutes = 4 hours. Since it's East, add time: 12:00 Noon + 4 hours = 4:00 PM)
- c) Equator
- d) 82°30' E
- b) It decreases
- a) Gain a day (They move into the previous day)
- b) 4 minutes
- d) The North and South Poles
Study these notes thoroughly. Understanding the relationship between the Earth's rotation, latitude, longitude, and time is crucial. Good luck with your preparation!