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NCERT Solutions for Class 9 Geography Chapter 7 Internationa...

NCERT Solutions for Class 9 Geography Chapter 7 International Date Line

Author at PW

June 28, 2025

NCERT Solutions for Class 9 Geography Chapter 7: NCERT books are very important for students. They help in school exams and also in future competitive exams like UPSC, SSC, and others. That’s why it is important to read the NCERT syllabus properly and understand each chapter well. These books explain topics in a simple and clear way, which helps students build a strong base in every subject.

To support your learning, we are providing NCERT solutions for all subjects and classes. Here, you will find the complete solution for Geography Class 9 Chapter 7, which is about the International Date Line. This chapter explains what is International Date Line, how it helps in managing time and date across the world, and why the International Date Line passes through the Pacific Ocean and bends around some places to avoid confusion.

The solutions below are written in simple steps to help you understand the topic easily. These answers will help you in revision, homework, and exam preparation. Check the detailed NCERT solutions for Chapter 7 below.

Check Out: Class 9th Books

NCERT Solutions for Class 9 Geography Chapter 7 International Date Line

Q 1. Two boxes in different hemispheres are given in the following diagram. The IDL passes through both the boxes. In one box, the meridian, day and date is given. Find the day and date for the other box.

Answer:

IDL

150 0 W Meridian, Monday 15th August 150 0 E Meridian, Tuesday, 16th August

80 0 W Meridian, Saturday, 24th December 170 0 E Meridian, Sunday 25 December

Q 2. Select the correct option:

(1) While crossing the IDL, a person will have to add one day when travelling from (a) East to West (b) West to East (c) South to North (d) North to South (2) If it is Wednesday 10 a.m. at 150 E meridian, then what will be the time at IDL? (a) Wednesday 6 a.m. (b) Wednesday 9 p.m. (c) Thursday 2 p.m. (d) Thursday 6 p.m. (3) According to the international convention, at which meridian does the day and date change occur? (a) 0 0 (b) 90 0 E (c) 90 0 W (d) 180 0 (4) At which direction of the IDL does a new day start immediately? (a) East (b) West (c) North (d) South (5) IDL brings coordination in which of the following? (a) GPS system (b) Defence departments (c) Transportation schedules (d) Determining the hemisphere

Answer 1: (a) East to West

Answer 2: (b) Wednesday 9 p.m.

Answer 3: (d) 180 0

Answer 4: (a) East

Answer 5: (c) Transportation schedules

Q 3. Give geographical reasons

(1) IDL is proving to be very useful in today’s times (2) The day starts in Pacific Ocean on the earth

Answer 1: The IDL brings coordination between international airlines, transportation service, economic and trade activities. It is important in today’s modern era and rapidly happening global development so that we can keep a track of all the calculations of day and time accurately. With the help of IDl global transportation especially airways the schedules of the traffic worldwide are organised properly.

Answer 2: The IDL passes through the Pacific Ocean. With reference to the IDL the day on earth starts in the west and ends in the East. It is one and the same day only at 12 o’clock midnight at the 180° meridian. For the countries lying to the east of it i.e. the USA, Chile, etc. it is the end of the day while for the countries lying to the west of it i.e. Japan, Australia, etc. it is the start of a new day. Thus, a new day starts in Pacific ocean on Earth.

Q 4. Write in brief:

(1) What considerations have been made while deciding the IDL? (2) While crossing the IDL, what changes will you make? (3) Why is the IDL not a straight line like the 180 0 meridian? (4) Why doesn’t the IDL pass through the land? (5) Why is the IDL considered with respect to the 180 0 meridian only?

Answer 1: Following points are taken into consideration while drawing an IDL

The direction of travel – The sun travels from east to west and the earth rotates from west to east. Thus, the countries in the west, 12.00 at midnight is the end of the day and the countries of the east, it is the start of the day.

Current day and date – When we travel across the meridian, the day and the date changes. While travelling from east to west, one day has to add to the day of commencing the journey. But while travelling from west to east, the same day is considered upon arrival.

Answer 2: The International Date Line runs down the middle of the Pacific Ocean. If you cross the dateline moving east, you subtract a day, whereas if you are moving west you add a day. For example, if today is Friday and we crossed the International Dateline from west to east then it would be Thursday. If we went east to west it would be Saturday.

Answer 3: If the line was straight, then it could pass through some territories and island groups. This will result in the increase of a day on the same island and a country which would create a massive confusion among the civilians. To prevent this confusion, the line is deviated roughly following the 180° line of longitude.

Answer 4: If the International Date Line did cross land, people crossing the line would have to adjust their clocks by twenty-three hours! People on opposite sides of the line would disagree about what day it was. For some strange reason, none of the countries near the International Date Line wanted to subject their citizens to that sort of complication.

Answer 5: According to the international conventions, the start of a date is considered to be at 180° meridian. This is because, when one crosses the 180° meridian from east or west, there is a difference of 12 hours from prime meridian. Accordingly, an adjustment or change in day time is made at 180° meridian. Due to these reasons, the IDL is considered with respect to the 180° meridian only.

Summary of International Date Line

1. Introduction to Time and Longitude

Class 9 Geography Chapter 7 introduces the concept of time based on the Earth’s rotation.
The Earth completes one full rotation (360°) in 24 hours, which means it rotates 15° every hour.
This forms the basis for dividing the Earth into time zones, each covering 15° of longitude.

2. What is International Date Line?

The International Date Line Class 9 chapter explains that the International Date Line (IDL) is an imaginary line that runs roughly along the 180° longitude in the Pacific Ocean.
It serves as the line where the date changes by one day when crossed.

3. Time Zones and Standard Time

The Earth is divided into 24 time zones, one for each hour of the day.
Every country follows a standard time based on a central meridian of their time zone.
India, for example, follows IST (Indian Standard Time), which is based on 82½° E longitude.

4. Purpose of the International Date Line

The main function of the International Date Line is to keep the calendar date consistent with time across the world.
When you cross the IDL from west to east, you subtract a day; when you cross from east to west, you add a day.

5. Why the Line is Not Straight

Although it mostly follows the 180° meridian, the IDL zigzags to avoid dividing countries and islands into two different calendar days.
This prevents confusion in timekeeping and daily activities for people living in those regions.

6. Real-World Example

For example, if it is Monday on the west side of the IDL, it will be Sunday on the east side.
This difference is important for travelers, global businesses, and international communication.

7. IDL and Global Travel

The chapter highlights the importance of the IDL in global travel.
Pilots and navigators must keep track of the date change when flying across the Pacific Ocean.

Benefits of Solving NCERT Solutions

1. Easy to Understand Concepts: NCERT solutions explain every answer in simple steps. This helps students understand the topic clearly. For example, if you're learning what is International Date Line, the solution explains it in a way that’s easy to follow and remember.

2. Based on CBSE Syllabus: These solutions follow the CBSE pattern. So if you're studying Class 9 Geography Chapter 7, you will learn exactly what is needed, including how the International Date Line passes through the Pacific Ocean and why it is important.

3. Good for Exam Preparation: Most questions in school exams come from NCERT books. Solving these questions helps you practice and feel confident. If you study the International Date Line topic through these solutions, you’ll be ready to answer it well in exams.

4. Helps in Homework and Quick Revision: NCERT solutions save time when doing homework. During exams, you can use them to quickly revise topics like the International Date Line and understand them again without confusion.

5. Useful for Future Exams Too: Many big exams like UPSC, NEET, and JEE ask questions from NCERT topics. So learning things like what is International Date Line from NCERT solutions helps you prepare for school and future exams at the same time.

Check Out: Class 9th Sample Papers

International Date Line FAQs

1. What is the International Date Line?

The International Date Line is an imaginary line, mostly along the 180° longitude in the Pacific Ocean, where the date changes by one day when crossed.

2. Why is the International Date Line important?

It helps maintain a standard calendar system across the world, making sure that all countries follow the same order of dates and days.

3. Where does the International Date Line pass through?

The International Date Line passes through the Pacific Ocean but is not a straight line. It bends to avoid splitting islands and countries into different dates.

4. What happens when you cross the International Date Line?

When you cross it from east to west, you add a day. When you cross it from west to east, you subtract a day.

5. Is the International Date Line the same as the Prime Meridian?

No, the Prime Meridian is at 0° longitude, while the International Date Line is around 180° longitude on the opposite side of the Earth.

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