Question

Read the given passage and answer the following questions.

A time zone is defined as a region throughout which the same standard time is followed. A Canadian scientist Stanford Fleming suggested 24 time zones, each 15 degrees wide, for the whole world, as the Earth takes 24 hours to complete one rotation. Therefore, one time zone differs from the next by one hour. Some adjustments have been made in certain places so that a city or country is not divided into two time zones. India is one of the few countries where the time difference between GMT and IST is not an integer, but an integer and 30 minutes. While crossing over to a time zone towards our east, we will set our watch, one hour ahead of our time for travel through each time zone and if we move to a time zone west of us, we will set our watch one hour behind us. Some countries having a larger east west extent, have more than one time zone. Russia covers eleven time zones while USA and Canada have five time zones each. The countries which have large north south extent, follow the concept of Daylight Saving Time (DST) during winters. Since in winters, the duration of the daylight becomes short, they set their watches ahead so as to save on the daylight. In summers, they set their watches back to normal.

1. In how many time zones does India lie? Does India follow the practise of daylight-saving time during winter? Why/Why not?
2. How many degrees of longitude does one time zone cover?
3. What is the time difference between GMT and IST?

Answer 1

1. India lies in two time zones because it spans over 30° of longitude (each time zone covering 15°), but India follows only a single standard time zone (Indian Standard Time - IST) for the sake of convenience. India does not follow the practice of daylight-saving time during winter because it lies in the tropical region, i.e., the countries with large north-south extent typically follow daylight-saving time to save daylight during winters, but India does not fall into this category.
2. One time zone covers 15 degrees of longitude. This is because the Earth completes a full rotation of 360 degrees in 24 hours, and therefore, 360°/24 = 15° per time zone.
3. The time difference between GMT and IST is 5 hours 30 minutes. IST is ahead of GMT by this interval because IST is calculated based on 82.5° E longitude (the central meridian of India), and since each degree represents 4 minutes of time difference (82.5 × 4 = 330 minutes), it results in 5 hours and 30 minutes ahead of GMT.