Class 8 Geography Chapter 1 Local Time and Standard Time answers

Std 8 Geog Ch 1 Local Time and Standard Time questions and answers

Exercise

Q 1. Complete the sentence by selecting the correct option:

(a) The earth requires 24 hours for one rotation. In one hour,

(i) 5 longitudes will face the sun

(ii) 10 longitudes will face the sun

(iii) 15 longitudes will face the sun

(iv) 20 longitudes will face the sun

Ans. 15 longitudes will face the sun

(b) To calculate the difference between the local times of any two places on the earth,

(i) the noon time at both the places should be known

(ii) the difference in degrees of their longitudes should be known

(iii) the difference in standard times of both the places should be known

(iv) Changes need to be made according to International Date Line

Ans. the difference in degrees of their longitudes should be known

(c) The difference between the local time of any two consecutive longitudes is

(i) 15 minutes

(ii) 04 minutes

(iii) 30 minutes

(iv) 60 minutes

Ans. 04 minutes

Q 2. Give geographical reasons:

(a) The local time is decided by the noon time.

Ans. The length of the shadow is shortest at noon. Therefore the local time is decided by the noon time.

(b) The local time at Greenwich is considered to be the international standard time.

Ans. For an international coordination between countries, the local time at Greenwich (Greenwich Mean Time) in England is considered to be the international standard time.

(c) The standard time of India has been decided by the local time at 82.5° E longitude.

Ans. The Indian Standard Time (IST) has been decided according to the 82° 30′ E longitude which passes through Mirzapur (near Allahabad, Uttar Pradesh). This longitude passes through the middle of the country with reference to its longitudinal extent. The local time at this longitude has been selected as the standard time of the whole country.

(d) Canada has 6 different standard times.

Ans. Geographically, Canada extends from 52⁰W to 141⁰ W. So, the time difference between the east and west is nearly 6 hours. If Canada selects a time zone in between the two, then the time difference would be 3 hours. Therefore Canada has 6 time zones, Pacific, Mountain, Central, Eastern, Atlantic and Newfoundland.

Q 3. Answer in brief:

(a) If it is 12 noon at 60°E longitude, then explain what would be the time at 30° W longitude?

Ans. The difference between the two longitude is 60°E – (- 30° W)

= 60 + 30

= 90⁰

1⁰ = 4 mins

90⁰ = ?

= 90 x 4

= 360 mins

= 360 ÷ 60

= 6 hours

When it is 12 noon at 60°E longitude then it will be (12 noon – 6) 6 am at 30° W longitude

(b) How is the standard time of a place determined?

Ans. The local time at the longitude which generally passes through the middle of the country is deemed to be the standard time for that country.

c) A football match being played at Sao Paulo, Brazil started in India at 6 am IST. Explain what would be the local time at Sao Paulo?

Ans IST of India is 82° 30′ E longitude and Sao Paulo passes through 46.63° W.

The longitudinal difference between the two places is

= 82.30° – (-46.63°)

= 82.30 + 46.63

= 128.93

1⁰ = 4 mins

∴128.93⁰ = ?

= 128.93 x 4

= 515.72 mins

= 515.72 ÷60

= 8.60 (note: you have to convert 0.60 which is in decimals

to mins i.e. 0.60×60 ÷100 =36 mins)

= 8.36 hours.

Since Sao Paulo is in the west of GMT it is behind India by 8.36 hours

So, when it is 6 am in India, it is 9.24pm in Sao Paulo

Q 4. If it is 10 pm on 21st June at Prime Meridian, write the dates and time at A, B and C in the table.

Place	Longitude	Date	Time
A	120⁰ E	22^nd June	6 am
B	160⁰ W	21^st June	11.20 am
C	60⁰ E	22^nd June	4 am

Ans:

Place A — 1⁰ = 4 mins.

∴ 120⁰ = ?

= 120 x 4 mins

= 480 mins

= 480 ÷60

= 8 hours

Since place A is on the east, it is ahead of Prime Meridian by 8 hours.

So, if it is 10 pm on 21^st June at Prime Meridian, then it is 6 am on 22^nd June.

Place B — 1⁰ = 4 mins.

∴ 160⁰ = ?

= 160 x 4 mins

= 640 mins

= 640 ÷60

= 10.67 hours

(Note: The decimal 0.67 is in unite which has to be converted to minutes, i.e. 0.67/100 x 60 = 0.40 mins)

Since place B is on the west, it is behind Prime Meridian by 10.40 hours.

So, if it is 10 pm on 21^st June at Prime Meridian, then it is 11.20 am on 21^st June.

Place C — 1⁰ = 4 mins.

∴ 60⁰ = ?

= 60 x 4 mins

= 240 mins

= 240 ÷60

= 4 hours

Since place C is on the east, it is ahead of Prime Meridian by 4 hours.

So, if it is 10 pm on 21^st June at Prime Meridian, then it is 2 am on 22^nd June.

Q 5. Write the situations of place A shown in these diagrams in the boxes below them :

(i) Sunrise (ii) midnight (iii) noon (iv) Sunset

(i) Midnight (ii) Sunset (iii) Sunrise (iv) Noon

Activity:

(a) Look for the actual granny’s clock in Shri Acharya Atre’s poem : “Aajiche Ghadyal “ ( granny’s clock). Look for this poem on the internet or in reference books.

Aajiche Ghadyal Kavi Keshavkumar kavita sangrah |

आजीचे घड्याळ

आजीच्या जवळी घड्याळ कसले आहे चमत्कारिक,
देई ठेवुनि तें कुठे अजुनि हे नाही कुणा ठाउक;
त्याची टिक टिक चालते न कधिही, आहे मुके वाटते,
किल्ली देई न त्यास ती कधि, तरी ते सारखे चालते

“अभ्यासास उठीव आज मजला आजी पहाटे तरी,”
जेव्हा मी तिज सांगुनी निजतसे रात्री बिछान्यावरी
साडेपाचही वाजतात न कुठे तो हाक ये नेमकी
“बाळा झांजर जाहले, अरवला तो कोंबडा, उठ की !”

ताईची करण्यास जम्मत, तसे बाबूसवे भांडता
जाई संपुनियां सकाळ न मुळी पत्त कधी लागता !
“आली ओटिवरी उन्हे बघ!” म्हणे आजी, “दहा वाजले !
जा जा लौकर !” कानि तो घणघणा घंटाध्वनी आदळे.

खेळाच्या अगदी भरांत गढुनी जाता अम्ही अंगणी
हो केव्हा तिनिसांज ते न समजे ! आजी परी आंतुनी
बोले, “खेळ पुरे, घरांत परता ! झाली दिवेलागण,
ओळीने बसुनी म्हणा परवचा ओटीवरी येउन !”

आजीला बिलगून ऐकत बसू जेव्हा भुतांच्या कथा
जाई झोप उडून, रात्र किती हो ध्यानी न ये ऐकता !
“अर्धी रात्र कि रे” म्हणे उलटली, “गोष्टी पुरे ! जा पडा !’
लागे तो धिडधांग पर्वतिवरी वाजावया चौघडा

सांगे वेळ, तशाच वार-तिथीही आजी घड्याळातुनी
थंडी पाऊस ऊनही कळतसे सारें तिला त्यांतुनी
मौजेचे असले घड्याळ दडुनी कोठे तिने ठेविले?
गाठोडे फडताळ शोधुनि तिचे आलो ! तरी ना मिळे !

_केशवकुमार

(b) Find out the velocity of the earth’s rotation in km/ hour.

Earth’s circumference at the equator = 40 075 km

One rotation = 23. 93 hrs

∴ Velocity of the Earth’s rotation = 16675 Km/hr

Extra Textual questions:

Let’s Recall

Why does the duration of day and night keep changing?

Ans. The duration of the day and night keeps changing due to the roation of the earth and its inclined axis.

How many longitudes can be drawn on a world map keeping an interval of 1° each?

Ans. The measure of the earth is 360°, so we can draw 360 longitudes on a world map, keeping an interval of 1° each.

The apparent movement of the sun from east to west is a result of what?

Ans. Since the earth rotates from west to east, the sun appears to move from east to west.

What is the direction of the rotation of the earth?

Ans. The earth rotates from west to east.

While the earth rotates, how many longitudes face the sun daily?

Ans.The Earth takes 24 hours i.e. one day to complete one rotation, so all the 360 longitudes face the sun daily.

At which longitude does the date change?

Ans. The date changes at 0° longitude

How was time measured in olden days?

Ans. In olden days, people used to take the help of various tools like sundial and hour glass and also depend on various natural events for the measurement of time.

In present times, what are the instruments used for time measurement?

Ans. Today we use different types of clocks like, mechanical clocks, quartz clocks, atomic clocks, digital clocks, etc.

Example 1

Mashad, a town in Iran, is located on the 60° E longitude. When it is 12 noon at Greenwich, calculate the local time of Mashad town.
Answer:
Statement: As we move towards the east of the Prime Meridian, the local time increases by four minutes for every longitude. (Mashad is located to the east of Greenwich.)

The difference between the longitudes of Greenwich and Mashad = 60°.

Difference in local time
= 60 × 4
= 240 minutes.
= 240 minutes ÷ 60 minutes
= 4 hours.

This implies that the time at Mashad would be 4 in the evening.

Example 2:
Manaus city in Brazil is located on 60° W longitude. What would be the local time at Manaus when it is 12 noon at Greenwich?
Statement: As we move towards the west of the Prime Meridian, the local time decrease by four minutes for every longitude. (Manaus is located to the west of Greenwich.)

The difference between the longitudes of Greenwich and Manaus = 60°.

Total difference in time = 60 × 4
= 240 minutes.
= 240 minutes ÷ 60 minutes
= 4 hours.

As Manaus is located to the west of Greenwich, the local time of Manaus is behind Greenwich time by 4 hours. Therefore, when it is noon at Greenwich, it would be 8 a.m. at Manaus.

Study the map given on page 4 of your text book and answer the following questions. Use the relation between degrees and time for this.

(1) Between which longitudes does the region experience daytime?

Ans. The regions between 90⁰E and 90⁰ W longitude experience daytime.

(2) Which longitudes experience noon and midnight respectively?

Ans. It is noon at 0⁰ longitude and midnight at 180⁰ longitude.

(3) Edward from New Orleans is on which longitude?

Ans. Edward from New Orleans is on 90⁰ w longitude.

(4) What is the time at Accra city?

Ans.It is noon at Accra city.

(5) At the same time, what is Sharad from Patna and Yakaito from Ans. Japan doing? What time is it in these cities?

At the same time at Patna it is 5pm, Sharad is returning from school and in Japan it is 9pm so Yakaita is getting ready to sleep.

(6) Select any one longitude. Calculate the local time of the longitudes lying 1° to the west and east of this longitude.

Ans. I have selected 75⁰w. It 5pm now at this place.

Therefore:

1⁰ W is behind by 4 minutes. So the time there is 4.56 pm

And 1⁰ E is ahead by 4 minutes. So it is 5.05 pm there.

What is the maximum number of local times that can there be in the world?

Ans. The world is divided into 24 time zones, therefore the maximum number of local times can be 24.

How many longitudes pass the sun in one hour?

Ans. One longitude takes 4 mins. to pass the sun, therefore in one hour (60 minutes )

4 mins = 1⁰

∴ 60 mins ( 1hr) = ?

∴ no of longitudes in one hour = 60/4

= 15⁰

= 15 longitudes.

Therefore, 15 longitudes pass the sun in one hour.

Use your brain power!

Tick the time in the boxes which you can tell without using clock.

Sunrise ✓ Sunset ✓

Noon ✓ Midnight X

Can you tell?

Mumbai is located at 73° E longitude. Kolkata is located at 88° E longitude. Find the difference between the longitudes of these two – cities.

Ans. The difference between the longitudes of Kolkata and Mumbai is 88 – 73 = 15⁰

If the local time at Mumbai is 3 pm then what would be the local time at Kolkata?

1⁰ = 4 minutes

∴ 15⁰ = ?

= 15 x 4

= 60 minutes

Since Mumbai is located at 73° E longitude and Kolkata is located at 88° E longitude. The time difference between the local times of Kolkata and Mumbai is one hour. Kolkata is on ahead of Mumbai by one hour. Therefore if it is 3 pm in Mumbai, it is 4 Pm in Kolkata.

Give it a try.

Look for the map of world time zones from reference books and see in which time zone India falls into?

Ans. India falls under the time zone of 82.5⁰ or GMT + 5.30 hours

With the help of an atlas find out which countries need more than one standard time.

Ans. Countries like France, USA, UK, Russia and Australia have more than one standard time.

Can you tell?

Look at the figure 1.4 given on page 6 of the textbook and answer the following questions:

1. Considering the longitudinal extent of India, how many longitudes with a difference of 1° can be drawn on a map?

Ans. India extends from 68⁰E to 98⁰E longitude, therefore with a difference of 1⁰ , India extends to 31 longitudes (98 – 67)

2) By how many minutes do two consecutive longitudes differ?

Ans. Two consecutive longitudes differ by 4 minutes.

3) What is the value of degrees of longitude at Mirzapur?

Ans. The value of the longitude at Mirzapur is 82.3⁰ E

4) If it is 8 a.m. at 82°30′ E, what would be the time in their clocks at the following places: Jammu, Madurai, Jaisalmer, Guwahati.

Ans. The Indian Standard Time (IST) has been decided according to the 82° 30′ E longitude which passes through Mirzapur (near Allahabad, Uttar Pradesh). Therefore, if it is 8 am in Mirzapur, then the whole of India will show 8 am in their clocks. So clocks in Jammu, Madurai, JAisalmer and Guwahati will show 8 am.

5. Though the distance between them is more why doesn’t the standard time differ in these places?

Give it a try.

1. If it is 8 a.m. in India, what is the time in Greenwich?

Ans. The Indian Standard Time (IST) has been decided according to the 82° 30′ E longitude and Greenwich lies on 0⁰ longitude. So there is a difference of 82.3 between the two longitudes

1⁰ = 4 minutes

∴ 82° 30′ = ?

= 82.3 x 4 mins.

= 329.2 mins.

= 5 hours 29 mins

India lies to the east of Greenwich, so India is ahead of Greenwich by 5 hours and 29 mins. Therefore, if it is 8 am in India, then it will be 2.31 am in Greenwich.

2. When it is 2 p.m. in India, in which countries would it be 2 p.m. too?

Ans. India follows 82° 30′ E longitude as its Standard Time. All the countries that follow this longitude as their standard time will have 2 pm too.

3. When it is 9 a.m. in India, what would be the time at 82° 30′ W longitude?

Ans. India follows 82° 30′ E longitude as its Standard Time. And 82° 30′ W longitude is exactly 180⁰ from India. Therefore, when it is 9 a.m. in India, the time at 82° 30′ W longitude would be 9 p.m.

4. What would be the time at Prime Meridian when a new day starts at 180° longitude?

When a new day starts at 180° longitude, the time at Prime Meridian would be 12 noon.

Think about it.

1. In which of the following countries, does only one standard time exist?

Mexico Sri Lanka New Zealand China

Ans. In Sri Lanka, New Zealand and China only one standard time exists.

2. Why does a country having a large latitudinal extent have only one standard time?

If there are different local times within a country because of longitudinal differences, then there will be a lack of synchronization in the routine activities in the country. If each one follows their local time, discrepancies emerge in carrying out daily business in the country. Therefore, generally, the local time at the longitude which generally passes through the middle of the country is deemed to be the standard time for that country. This standard time is used all over the country. Normally, if the difference between the longitudinal extent of the country is less than one or two hours, only one standard time is considered for the country. But if the longitudinal extent (east-west extent) is more than that, then, one standard time is not enough and in such countries, more than one standard time zones are considered.