Kerala Syllabus STD 8 Social Science: Chapter 03 Movements of the Earth: Rotation and Revolution - Questions and Answers | Teaching Manual | Teachers Handbook


Study Notes for Class 8 Social Science (English Medium) ഭൂമിയുടെ ചലനങ്ങൾ: ഭ്രമണവും, പരിക്രമണവും | Text Books Solution Social Science (English Medium) Chapter 03 Movements of the Earth: Rotation and Revolution | Teaching Manual & Teachers Handbook 

എട്ടാം ക്ലാസ് Social Science ലെ Unit 3 Movements of the Earth: Rotation and Revolution - Complete Questions and Answers. പഠന സഹായികൾ അയക്കാൻ താല്പര്യമുള്ളവർ ഈ നമ്പറിൽ വാട്സാപ്പ് ചെയ്യുക: 9497346250. 

Chapter 03: Movements of the Earth: Rotation and Revolution - Questions and Answers 
∎Std 8 Social Science
♦ Why do we feel that the sun rises in the east and sets in the west?
The direction of rotation of the Earth is from the west to the east. That is why we feel that the sun rises in the east and sets in the west.

♦ What are the two main effects of the rotation of the Earth?
• Day and night 
• Coriolis effect

♦ What is called the Circle of Illumination?
The imaginary line that demarcates day and night on the Earth is called the Circle of Illumination.

♦ What is the time taken for the Earth to complete one rotation?
24 hours (23 hours 56 minutes 4 seconds)

♦ What is known as the Coriolis Force? What is called the Coriolis Effect?
Due to rotation, freely moving bodies on the Earth's surface get deflected in their direction. The force responsible for this deflection is known as Coriolis Force and the deflection in direction is called Coriolis Effect.

♦ Define Ferrel's law
Admiral Ferrel discovered that due to the Coriolis Effect,ocean currents and winds change their direction in the northern hemisphere to the right and in the southern hemisphere to the left. This is known as Ferrel's law.

♦ Some facts related to rotation are given below. Complete the table by finding out the reasons behind these facts
Important lines of latitude  Measure in degrees
• The Sun rises in the east and sets in the west.The direction of rotation of the Earth is from the west to the east
• Freely moving bodies get deflected in their direction in both hemispheresCoriolis Force
♦ What is known as Revolution?
While rotating on its axis, the Earth revolves around the Sun in a fixed orbit. This is known as Revolution.

♦ What is the time taken to complete one revolution in the elliptical orbit?
365¼ days

♦ What is a leap year?
The year which has 366 days.
Eg:2024,2028,2032,2036

♦ Difference between Perihelion and Aphelion?
• The day on which the Earth comes closest to the Sun during revolution (147 million kilometres) is known as Perihelion. This happens in the month of January (around 3rd January).
• The distance between the Sun and the Earth will be at a maximum (152 million kilometres) in the month of July (around 4th July). This is called Aphelion

♦ What do you meant by the apparent movement of the Sun?
Since the tilt of the earth’s axis is maintained at an angle of 23½ degree throughout the revolution, the Sun’s apparent position moves northward and southward between the Tropic of Cancer and the Tropic of Capricorn. This apparent shift in the Sun’s position is called the apparent movement of the Sun.
♦ Effects of the apparent movement of the Sun
The duration of day and night changes

♦ On which latitude do the Sun’s rays fall vertically? 
Zero degree latitude(Equator)

♦ On which days does this happen?
21st March and 23rd September

♦ What are called equinoxes? Classify equinoxes and write a note.
During the Revolution, on 21st March and 23rd September, the sun’s rays fall vertically on the equator. The duration of day and night will be equal on both hemispheres on these days. These days are called equinoxes. 
21st March is known as Spring Equinox and 23rd September is Autumnal Equinox.

♦ In which direction does the apparent position of the sun shift from 21st March onwards?
Towards north from the Equator to the Tropic of Cancer

♦ On which latitude do the sun’s rays fall vertically on 21st June?
Tropic of cancer

♦ What will be the duration of the night in the southern polar regions when there is daylight for six months in the northern polar regions?
Six months

♦ In which direction does the Sun’s apparent position shift from 23rd September onwards?
Southward Direction

♦ On which latitude do the Sun's rays fall vertically on 22nd December?
Tropic of Capricorn

♦ Write a short note about the Summer Solstice.
In the northern hemisphere, the Sun’s apparent position shifts towards north from the Equator to the Tropic of Cancer from 21st March to 21st June. As a result of this on 21st June, the northern hemisphere experiences the longest day and the shortest night. This day is known as summer solstice. 

♦ Write a short note about the Winter Solstice.
In the southern hemisphere the Sun’s apparent position shifts from the equator to the Tropic of Capricorn during the period from 23rd September to 22nd December. As a result of this, on 22nd December, the southern hemisphere experiences the longest day and the shortest night. This day is known as the Winter Solstice. 

♦ Explain what is Uttarayanam and Dakshinayanam?
• Following the winter solstice (December 22) the apparent movement of the Sun from Tropic of Capricorn (23½0 South) to Tropic of Cancer (23½0 North) is known as the apparent movement of the Sun towards North (Uttarayanam).
• The shift in the apparent position of the Sun after the Summer Solstice (June 21) from the Tropic of Cancer (23½0 North) to Tropic of Capricorn (23½0 South) is known as the apparent movement of the Sun towards South (Dakshinayanam).

♦ Complete the table.
♦ What are seasons? Reason for the occurrence of the seasons?
• Due to the apparent shift in the position of the Sun, different places experience specific weather patterns. These patterns are known as seasons.
• The revolution of the Earth and variations in the availability of solar energy is the reasons for the occurrence of the seasons.
♦ What is called seasonal change?
The occurrence of spring, summer, autumn and winter in a cyclical manner during a year is called seasonal change.

♦ Make a table on different seasons and their characteristics
Seasons Characteristics
• Spring• plants bloom and produce fruits
• During this period duration of daytime gradually increases
• Summer• high atmospheric temperature
• generally longer days
• Autumn• trees shed their leaves before the arrival of winter
• during this period duration of daytime gradually decreases
• Winter• low atmospheric temperature
• snowfall
• generally longer nights
♦ Observe the table about the different seasons in northern and southern hemispheres and write the answers for the questions given below.
• What change happens to the apparent movement of the Sun when it is summer season in the northern hemisphere?
The sun's apparent position shifts from the Tropic of Cancer to the equator

• What will the season be in the northern hemisphere when it is autumn in the southern hemisphere? 
Spring is experienced in the Northern Hemisphere

• Which season is experienced in the southern hemisphere from 23rd September to 22nd December?
Spring is experienced in the Southern Hemisphere

• Name the season in the southern hemisphere when the Sun's apparent position shifts from the Tropic of Capricorn to the equator.
Summer is experienced in the Northern Hemisphere

♦ What is Local time?
The time calculated based on the length of the shadow and position of the Sun is termed as the Local time.

♦ What is the problem faced if there be different local times within a country?
This will create confusion for commonly conducted examinations, railway time, radio telecast etc.

♦ Importance of Greenwich Mean Time
The longitude that passes through the Royal British Observatory in England is taken as zero-degree meridian. This is called Prime Meridian. The local time at Prime Meridian is called the Greenwich Mean Time. Travellers worldwide calculate time based on Greenwich Time. As the rotation of the Earth is from the west to the east, as we move each longitude east of Greenwich, 4 minutes is added and towards the west 4 minutes is subtracted. 

♦ What do travellers worldwide use to calculate time?
Greenwich Mean Time

♦ What is the local time at the Prime Meridian called?
Greenwich Mean Time

♦ How does the time difference change east and west of Greenwich Mean Time?
As the rotation of the Earth is from the west to the east, as we move each longitude east of Greenwich, 4 minutes is added and towards the west 4 minutes is subtracted. 

♦ Name the longitude that passes through the Royal British Observatory in England?
Zero degree meridian (Prime Meridian).

♦ What will be the time at 1° East and 1° West when it is 10:00 A.M. at Greenwich Meridian (0° longitude)?
♦ When it is 9.00 P.M. at Greenwich Meridian (0° longitude), what will the time be at 30° East?
♦ What is Standard Time?
The local time at the Standard Meridian is considered the standard time of the country.
♦ Explain the importance of Standard Time?
The local time at each longitude will be different. If different local times exist within a country, it will create confusion for commonly conducted examinations, railway time, radio telecast, etc. To overcome this crisis, based on an international understanding, countries have selected a longitude, which is a multiple of 7½° longitude as Standard Meridian. The local time at this Standard Meridian is considered as the standard time of the country.

♦ Standard Time of India
The 82 ½° E longitude is considered the standard meridian of India. The local time along this longitude is generally considered as the common time of India. This is known as the Indian Standard Time.

♦ Standard Meridian 
Based on an international understanding, countries have selected a longitude, which is a multiple of 7½° longitude as the Standard Meridian.

♦ The Standard Meridian of India
82½0 East longitude

♦ What is the time difference between Greenwich Meridian and Indian Standard Meridian (82½° East)?
5.30 hours

♦ What is the time difference between India’s easternmost state, Arunachal Pradesh, and the westernmost state Gujarat.
About two hours

♦ What are time zones?
Based on international understanding, the world has been divided into 24 zones with 1 hour difference. These are time zones. Each time zone has 15° longitudinal distance

♦ Write examples for countries with large longitudinal extensions have many time zones and Standard Time.
Russia, the USA, and Australia

♦ Figure 3.23 What is the time and date at 180° East and 180° West when it is December 25 evening 6 p.m. at Greenwich Meridian?
• 180° Eat - 6 A.M on December 26
• 180° Eat - 6 A.M on December 25

♦ Write a short on the International Date Line?
• Based on international agreement, 180° longitude is considered the International Date Line. 
• The time difference between east and west sides of 180° longitude is 24 hours.
• Travellers who move westwards crossing the line add a day, and the travellers who move towards the east calculate time by deducting a day.


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