Class 8: Subject :Geography 1.Local time and Standard Time.

Class 8: Subject :Geography 

1.Local time and Standard Time.

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

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

(a) 5 longitudes will face the sun

(b) 10 longitudes will face the sun

(c) 15 longitudes will face the sun

(d) 20 longitudes will face the sun

Answer:(c) 15 longitudes will face the sun

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

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

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

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

(d) changes need to be made according to International Date Line.

Answer:(b) the difference in degrees of their longitudes should be known

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

(a) 15 minutes(b) 04 minutes(c) 30 minutes(d) 60 minutes

Answer:(b) 04 minutes

Q. 2 Give geographical reasons for the following.

1. The local time is decided by the noon time.

Ans. (1) When at a particular place, the sun reaches the maximum height in the sky it is assumed that almost half of the daytime is over and this time is considered 12 noon.

(2) The time of a particular place as decided by the overhead position of the sun in the sky is considered as the local time of that place.

(3) During the rotation of the earth, when a particular longitude comes exactly in front of the sun, it is considered as noon time (12 noon) on that longitude. This noon time is considered as local time of that longitude. In this way, the local time is decided by the noon time.

2. The local time at Greenwich is considered to be the International Standard Time.

Ans. (1) The International Standard Time has been decided according to 0° longitude.

(2) 0° longitude passes through Greenwich, England.

(3) For an international coordination, it is essential to bring compatibility between the standard times of various countries in the world. For this purpose, the local time at Greenwich is considered to be the International Standard Time.

3. The standard time of India has been decided by the local time at 82°30' E longitude.

Ans. (1) With respect to the longitudinal extent, 82°30' E longitude passes through the middle of India.

(2) The difference between the local time at 82°30' E longitude and the local time at the extreme east and west longitude passing through India is not more than one hour. Therefore, the standard time of India has been decided by the local time at 82°30' E longitude.

4. Canada has 6 different standard times.

Ans. (1) The longitudinal extent of Canada is between 52°37' W and 141° W.

(2) Thus, the difference between the extreme east and west longitude passing through Canada is of 88 degrees.

(3) The difference between the local time at extreme east and west longitude passing through Canada is of 352 minutes i.e. 5 hours and 52 minutes. Therefore, it is not practically helpful to consider single standard time in Canada. Therefore, for synchronizing the routine activities in the country, Canada has 6 different standard times.

Q. 3. Answer in brief:

1. If it is 12 noon at 60° E longitude, then explain what would be the time at 30° W longitude.

Ans. (1) The difference between 60° E longitude and 30° W longitude will be of 90 degrees. (The difference of 60 degrees between 0° and 60° E + the difference of 30 degrees between 0° and 30° W = 90 degrees.)

(2) Difference in local time

= 90 × 4

= 360 minutes.

= 360 minutes / 60 minutes

= 6 hours.

(3) Longitudes lying to the east of any longitude are ahead of the time of that longitude while those lying to the west are behind.

(4) Therefore, if it is 12 noon at 60° E longitude, then it would be 6 a.m. at 30° W longitude. (behind by 6 hours)

2. How is the standard time of a place determined?

Ans. (1) The local time at the longitude passing through the middle of a country / place is generally considered as a standard time of that country / place.

(2) If the difference between the local time at the extreme east and west longitude passing through a country is less than one or two hours, one standard time is considered for a country. Thus, there exists only one standard time in a country having comparatively less longitudinal (east-west) extent.

(3) If the difference between the local time at the extreme east and west longitude passing through a country is more than one or two hours, more than one standard time zones are considered for a country. Thus, there exists more than one standard time zones in a country having comparatively more longitudinal (east-west) extent.

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

Ans. (1) Statement : For any longitude lying to the west of particular longitude, the local time decreases by 4 minutes for every longitude. (Sao Paulo is located to the west of India)

(2) The difference between the longitudes of Sao Paulo and India = 127°30'.

(3) Difference in local time

= 127.5 × 4

= 510 minutes.

= 510 minutes / 60 minutes

= 8 hours 30 minutes.

(4) Thus, if it is 6 a.m. at India, it would be 9.30 p.m. of the previous day at Sao Paulo. Therefore, if a football match being played at Sao Paulo, Brazil started in India at 6 a.m. IST, the local time at Sao Paulo would be 9.30 p.m. of previous day.

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. 

Answer :

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

Answer: