Local Time and Standard Time
Chapter 1 — Chapter Test Solutions
Complete the sentence by selecting the correct option:
(a) The earth requires 24 hours for one rotation. In one hour,
(b) To calculate the difference between the local times of any two places on the earth,
(c) The difference between the local time of any two consecutive longitudes is
Give geographical reasons:
(a) The local time is decided by the noon time.
Ans:
- The local time of a place is fixed with reference to the apparent movement of the sun.
- When the sun is directly overhead in the sky, it is midday or noon.
- The noon time is the same at any point along a given longitude, from the North Pole to the South Pole.
(b) The local time at Greenwich is considered to be the international standard time.
Ans:
- Greenwich is located at 0° longitude in London.
- When the sun is at its highest point exactly above the Prime Meridian, it is noon at Greenwich.
- The local time increases by 4 minutes for every longitude to the west of Greenwich, and decreases by 4 minutes for every longitude to the east of Greenwich.
- Since people living across many different longitudes interact with each other, an International Standard Time helps avoid chaos and confusion.
(c) The standard time of India has been decided by the local time at 82.5°E longitude.
Ans:
- 82.5°E longitude passes through the middle of the country, with reference to its longitudinal extent.
- When the sun is directly overhead on this longitude, it is assumed to be 12 noon across India.
- There is no difference of more than one hour between the local time at 82.5°E and the local time at any other place in the country.
(d) Canada has 6 different standard times.
Ans:
- If the difference in longitudinal extent of a country is less than one or two hours, the country generally has only one standard time.
- The longitudinal (East-West) extent of Canada spans about four and a half hours.
- From west to east, Canada’s six time zones are: Pacific, Mountain, Central, Eastern, Atlantic and Newfoundland.
Answer in brief:
(a) If it is 12 noon at 60°E longitude, what would be the time at 30°W longitude?
Ans:As we move east of the Prime Meridian, local time increases by 4 minutes for every degree of longitude. As we move west of the Prime Meridian, local time decreases by 4 minutes for every degree of longitude.
(b) How is the standard time of a place determined?
Ans:
- Standard time is determined on the basis of the time zones into which the earth is divided.
- Standard time is the same throughout a particular country, as it is fixed by the law of that country.
- It is determined by the distance, east or west of the Prime Meridian at Greenwich, of a chosen longitude lying within that region.
(c) A football match being played at São Paulo, Brazil started in India at 6 a.m. IST. What would be the local time in São Paulo?
Ans:If it is 10 p.m. on 21st June at the Prime Meridian, write the dates and times at A, B and C in the table.
Ans:| Place | Longitude | Date | Time |
|---|---|---|---|
| A | 120°E | June 22 | 6.00 a.m. |
| B | 160°W | June 21 | 11.20 a.m. |
| C | 60°E | June 22 | 2.00 a.m. |
Write the situation of place A shown in each diagram: sunrise, midnight, noon, sunset.
Ans: