Kerala Syllabus 10th Standard Social Science Solutions Chapter 1 Seasons and Time

Kerala State Syllabus 10th Standard Social Science Solutions Chapter 1 Seasons and Time

Question 1.
Identify the factor not responsible for the occurrence of seasons from among the following.
a. Revolution of the earth
b. Tilt of the earth’s axis
c. Parallelism of the earth’s axis
d. Rotation of the earth
d. Rotation of the earth

Question 2.
The sun’s rays fall vertically between Tropic of Cancer and Tropic of Capricorn. Why?
The movement of the earth around the sun in a fixed orbit is known as revolution. During revolution, the apparent position of the sun in relation to earth varies. The sun shifts apparently between Tropic of Cancer (23$$\frac { 1 }{ 2 }$$°N) and Tropic of Capricorn (23 $$\frac { 1 }{ 2 }$$°S). The position of the sun will be over the equator on March 21, over the Tropic of Cancer on June 21, over the equator again on September 23 and over the Tropic of Capricorn on December 22.

Thus the position of the sun in relation to earth varies apparently between Tropic of Cancer and Tropic of Capricorn. This is known as the apparent movement of the sun. As a result, Sun’s rays fall vertically between Tropic of Cancer and Tropic of Capricorn.

Question 3.
Explain the geographical importance of March 21, June 21, September 23 and December 22.

March 21 and September 23: The apparent position of the sun during the earth’s revolution will be over the equator on March 21 and September 23. So equal amount of sunlight is received in both the hemispheres. Hence the length of day and night will be equal on these days in both the hemispheres. These days are called equinoxes.

June 21: From March 21 onwards, the sun apparently shifts from the equator northwards and leaches vertically over the Tropic of Cancer on June 21. This day is known as summer solstice in the Northern Hemisphere. On this day the Northern Hemisphere experiences the longest day and the shortest night and the Southern Hemisphere the longest night and the shortest day.

December 22: The apparent position of the sun shifts from the equator from September 23 and reaches vertically over the Tropic of Capricorn on December 22. This day is known as winter solstice in the Northern Hemisphere. On this day, the Northern Hemisphere experiences the shortest day and longest night and the Southern Hemisphere experiences the longest day and the shortest night.

Question 4.
Why is there an eastward increase and westward decrease in time?
As the earth rotates from west to east, time advances towards the east and recedes towards the west. From a definite longitude, the time is estimated to increase by 4 minutes towards the east and decrease by 4 minutes towards the west for every degree of longitude. Since the rotation is from west to east, the sunrise is first experienced in the eastern part of a region.

Question 5.
Why is the International Date Line not straight unlike other longitudes?
The 180° longitude line from the east and west of Greenwich line is the International Date Line. There is a time difference of 24 hours on both the sides of this line. It creates much difficulty if the same place records two different times with 24 hours difference.

To avoid this, certain adjustments have been made avoiding the land area along the 180° longitude. The line is in such a way that it passes through Bering Strait in the Pacific Ocean and avoids some of the inhabited islands. So the International Date Line is not a straight line. The travellers who cross this line from the west calculate time by advancing it by one day and those who cross the line from the east deduct one day.

Question 6.
There is periodic variation in the amount of sunshine over different places in both the hemispheres of the earth. Why?

• Earth’s revolution
• Tilt of the earth’s axis
• Parallelism of the earth’s axis.

Question 7.
How much time does the earth take to complete the revolution?
One year or 365$$\frac{1}{4}$$ days.

Question 8.
What is a leap year?
A year in which February has 29 days.
Find out the leap years from 2000 to 2014.

• Leap years:2000,2004,2008,2012 – N
• After:2016,2020,2024,2028
• Leap year occurs once in 4 years.
Identify the days on which sun is closest and farthest from the earth.
• The earth comes closest to sun on January 3 and the distance is 147 million km. This day is known as perihelion.
• The earth is farthest from the sun on July 4 and the distance is 152 million km. This day is known as aphelion.

Question 9.
What will be the corresponding season in the Southern Hemisphere when it is summer in the Northern Hemisphere?
It is winter in the Southern Hemisphere because the amount of solar energy received here will be less.

Question 10.
The change of season is not explicit in Kerala. Why?
Kerala lies near the equator. So the seasonal change is not explicit here. Here the summer is hot while the winter is not very severe. High temperature is experienced on almost all days and so the amount of rainfall is also high. There is no marked difference in the length of day and night.

Question 11.
The frigid zones do not experience all the seasons. Discuss the reason.
In frigid zones, generally, summer season and winter season are experienced. The summer season here is cold and winter season is very severe. The northern frigid zone experiences continuous daylight for six months when the sun is in the Northern Hemisphere and the southern frigid experiences continuous night for 6 months.

From September to March when the sun is in the Southern Hemisphere, north polar or frigid zone experiences continuous night for six months and south polar region experiences continuous daylight for six months.

Question 12.
What is the peculiarity of day and night in the Southern Hemisphere on June 21?
On June 21, the Southern Hemisphere experiences its longest night and shortest day.

Question 13.
What is the peculiarity of the day and night in the Southern Hemisphere on 22 December?
On December 22, the Southern Hemisphere experiences its longest day and shortest night.

Question 14.
What is the season in the Southern Hemisphere when it is autumn in the Northern Hemisphere?
Spring season

Question 15.
What are the peculiarities of winter season?

• Winter season is severe in temperate and frigid zones.
• Severe cold and snowfall.
• Temperature falls below 0°C.

Question 16.
What might be the length of the day and night on the winter solstice day?
On December 22, the winter solstice day, the sun will be vertically above the Tropic of Capricorn. So nights would be longer and days would be shorter in the Northern Hemisphere. But in the Southern Hemisphere, days would be longer and nights would be shorter.

Question 17.
If the earth’s axis was not tilted, would there be alternate summer and winter in both the hemispheres?
If the earth’s axis was not tilted, the position of the sun would be always over the equator. If so, both the hemispheres would have received equal amount of sunlight throughout the year. There would not have been change in season on earth.

Question 18.
How is the duration of days and nights experienced at places within the Antarctic Circle while the sun is in the Southern Hemisphere?
When the sun is in the Southern Hemisphere, continuous daylight is received for six months throughout in the places within the Antarctic Circle. Days are longer and nights are shorter.

Question 19.
What is the change that occurs in the duration of day in the Northern Hemisphere during Dakshinayanam?

• Duration of day decreases.
• Duration of night increases.

Question 20.
What is the duration of day and night in the south polar regions when the sun is respectively over the Northern Hemisphere and Southern Hemisphere?

• When the sun is over the Northern Hemisphere, the south polar regions experience long nights and short days.
• When the sun is over the Southern Hemisphere, the south polar regions experience long days and short nights.

Question 21.
Is the local time in all the Indian states the same?
The local time of each longitude varies. The local time of all the Indian states is different. This creates difficulty and confusion. To avoid this, the local time of the meridian that goes through the centre of a country is taken as the common time for the whole country.

Question 22.
What will be the hardships if there are several local times in a country?

• Cannot prepare a railway time table applicable. throughout the country.
• Cannot give information on radio programmes.
• Cannot conduct a national level examination at a common time.

Question 23.
The people of which Indian state sees the sun first?
The people of Arunachal Pradesh. The eastern part of any country sees the sun first. Arunachal Pradesh is the easternmost state of India.

Question 24.
What would be the longitudinal extent of each time zone?

• 15° longitudinal extent
• Time difference is 1 hour.

Question 25.
Find the difference between the Indian Standard Time and the Greenwich Mean Time.
The longitude of Greenwich is 0°. The standard meridian of India is 82 $$\frac { 1 }{ 2 }$$°E or 82° 30 minutes. The longitudinal difference between India and Greenwich is 82$$\frac { 1 }{ 2 }$$°. Time difference for 15° longitude is 1 hour. Time difference for 82$$\frac { 1 }{ 2 }$$°
Longtiude = $$\frac{82^{\circ} 30 \text { minute }}{15}$$ = 5 hours 30 minutes
As India is located to the east of Greenwich, the time in India will be 5 hours 30 minutes ahead of Greenwich Mean Time.

Question 26.
The countries with wide longitudinal extent need to calculate time on the basis of more than one standard meridian. Why?
Each country in the world considers the longitude that passes through its middle as the standard meridian. The local time of the standard meridian is the common time for the eastern and western parts of the nation. If the time difference between the rising and setting of the sun in the eastern and western part of a nation is more than 2 hours usually, it leads to many difficulties and confusion. They are nations with wide longitudinal extent and so they take more than one standard meridian.

Time Zones:
There are 24 time zones in the world. Each time zone covers 15° of longitude. Russia has 11 time zones. USA has 5 time zones.

Question 27.
Why is the 82$$\frac { 1 }{ 2 }$$°E longitude considered as the standard meridian of India?
The longitudal extent of India is from 68°E and 97°E. This amounts to 30°. 82$$\frac { 1 }{ 2 }$$° E longitude passes almost through the middle of these longitudes. So it has been fixed as the standard meridian of India. The line passes through Mirzapur near Allahabad in Uttar Pradesh.

Question 28.
Calculate the time at each 15° longitude east and west of the Greenwich line up to 180° longitude.