SEBA Class 7 Social Science (English Medium) Chapter 1 – Calculation of Time on Earth Solutions & Summary
Explore SEBA Class 7 Social Science Chapter 1 – “Calculation of Time on Earth” solutions, designed for English medium students. This chapter introduces essential concepts related to timekeeping on Earth, including the Earth’s rotation, revolution, and how these motions create day and night. The lesson explains the different units of time such as seconds, minutes, hours, days, weeks, months, and years. Students will also learn about time zones and how they are based on the Earth’s rotation, as well as the significance of the International Date Line in determining the correct date across the globe. The chapter further covers the creation and use of the calendar system, which tracks the Earth’s revolution around the Sun, marking the passage of time and the changing seasons. Our detailed solutions include NCERT-based textbook answers, multiple-choice questions (MCQs), and a chapter summary that will help students develop a clear understanding of the topic. These resources are designed to help students excel in their exams and improve their comprehension of time calculations.
Class 7 Social Science (English Medium) PDF Solutions 2025-26 | SCERT Assam
Class 7 Social Science
Chapter – 1 Ospin Academy
Calculation of Time on Earth
Exercise:
1. Answer in brief:
(a) What is the total number of the longitude on earth at 1° interval?
Ans: The number of longitudes at 1° intervals can be calculated using the formula:
Total number of longitudes = 360°1° = 360
Total number of longitudes = 360°/1° = 360°.
So, there are 360 longitudes on Earth at 1° intervals.
(b) What is the longitude of Indian Standard Time?
Ans: The Indian standard time is calculated based on the longitude 82.5° meridian which passes near Allahabad.
(c) How many hours does the earth need to make a complete rotation of 360°?
Ans: The earth need 24 hours to complete a rotation of 360°.
(d) What is the value of in 0° of the prime meridians passing through Greenwich?
Ans: The value of the Prime Meridian passing through Greenwich is 0° longitude.
(e) What is the unit of angular distance?
Ans: The unit of angular distance is degrees or radians.
2. Fill in the blanks:
(a) The circumference of the earth makes an angle of ________ at its centre.
Ans: 360 degrees.
(b) The measurement of the line of longitude is called________.
Ans: Longitude.
(c) The angular distance of the Prime Meridian is ______ longitude.
Ans: 0 degrees.
(d) If a place remains away by 15°E from the mid-day sun, then the time at that place will be ______ hrs.
Ans: 1 hour ahead.
3. Say whether the following statements are true or false:
(a) As a result of the diurnal motion of the earth, the western places face the sun earlier than the places in the eastern side.
Ans: False.
(b) The travellers at the moment of crossing 180° from the east have to add up a day in their time schedule.
Ans: True.
(c) When it is 12 mid-night in any place on earth it indicates the end of a day and beginning of another day.
Ans: True.
(d) The time difference at 180° longitude is 12 hrs.
Ans: True.
(e) A place where evening occurs lately than in Greenwich is located in west longitude.
Ans: False.
4. Choose the correct answers:
(a) A traveller will have the feeling of loss/ gain in his time, if he moves to the west of Greenwich as per the GMT.
Ans: Gain.
(b) Mumbai has early sunrise than Greenwich therefore Mumbai is located at the east/west longitude.
Ans: East.
(c) Time in each longitude to the east of the Prime Meridian goes ahead/back by four minutes.
Ans: Ahead.
(d) The east longitude of 83°20′/90/82°30′ is accepted as the Indian Standard longitude.
Ans: 82°30′.
(e) The common watch that we wear runs according to the Greenwich Mean Time/ Indian Standard Time.
Ans: Indian Standard Time.
5. Write down the differences between-
(a) Latitudes and Longitudes.
Ans:
|
Latitudes |
Longitudes |
|---|---|
|
(i) Some lines in parallel with the equator from the east to the west direction are imagined towards the North Pole and the South Pole. These lines are known as Parallels of latitude. |
Longitude is a geographic coordinate that describes the east-west location of a location on the Earth’s surface or a celestial body’s surface. |
|
(ii) The calculation or measurement of the latitudes is known as parallels. |
The measurement of the meridians is called the longitudes. |
|
(iii) The angle made at the centre of the earth by two places residing on the surface of the globe ic called the angular distance between the two places. |
An angle is created by imagining line from this point towards the centre along with a line from another definite point of the equator connecting at the centre. |
(b) Local Time and Standard Time.
Ans:
|
Local Time |
Standard Time |
|---|---|
|
(i) The eastern place has earlier sunrise, noon and sunset than the western place. Time is calculated on the earth surface by analysing the position of the sun, and it is called the “Local time of that place. Different places located at different longitude have different local times. The local time of the prime meridian is termed as the “Greenwich Mean Time” (GMT). To calculate the local time of various places on the earth surface, GMT of the Prime Meridian has been accepted as a point of reference and for this we should know the longitude of that place. |
The local time of a line of longitude passing mid- way through the country has been accepted for calculation of time of the entire country. The line of longitude or a meridian is taken as the Standard Meridian, and the time in the country is called the Standard Time. In India, the standard time is calculated on the basis of the local time of 82.5° meridian which passes near Allahabad. This is known as the Indian Standard Time (IST). |
6. Solve the following problem-
(a) When it is 7 hrs in Greenwich (as per the GMT), then in a particular place, it is 12 noon. Find out the longitude of that place.
Ans: (b) A wireless message was sent from New York (75°W) city to Los Angeles (180°W) at about 12 noon. At what time was the message sent as per the local time of Los Angeles?
(c) What will be the exact time of a game to be held in Dhubri (90°E) as per its local time, when the same can be held in New Delhi (77°E) at 9 A.Μ.
Q1: What is the primary focus of Chapter 1 – “Calculation of Time on Earth”?
A: The primary focus of this chapter is to understand how time is calculated based on the Earth’s rotation and revolution, and the creation of time zones and calendars.
Q2: How do time zones relate to the Earth’s rotation?
A: Time zones are established based on the Earth’s 24-hour rotation, dividing the globe into regions that observe the same local time.
Q3: What role does the International Date Line play in time calculation?
A: The International Date Line helps determine the date in different time zones, ensuring consistency in timekeeping across the world.
Q4: Why is the calendar system essential in timekeeping?
A: The calendar system helps us track the passage of time through days, months, and years, which are tied to the Earth’s revolution around the Sun.
Q5: Where can I find solutions for all Social Science chapters of Class 7?
A: For solutions to all chapters, Click Here
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