Chapter 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,
 (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

(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

(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

Q 2. Give geographical reasons:

(a) The local time is decided by the noon time.
Ans. (1) The local time of a place on the earth’s surface is determined with reference to its noon time. (2) The noon time is the same at any given longitude across the earth i.e. from the north pole to the south pole. (3) Therefore, the local time is decided by noon time.

(b) The local time at Greenwich is considered to be the international standard time.
Ans. (1) The local time at Greenwich is considered to be the international standard time because, the Prime Meridian passes through Greenwich, England. (2) The Prime Meridian divides the globe into two equal sections making it easier to calculate the time. (3) Prime Meridian at Greenwich passes through longitude 0°. (4) Hence the Prime Meridian passing through Greenwich 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. (1) The 82.5°E longitude passes through the middle of India. (2) This longitude divides India into almost two equal sections. (3) It passes through Mirzapur (near Allahabad, Uttar Pradesh) (4) So, the local time at 82.5°E has been selected as the standard time of the whole country.

(d) Canada has 6 different standard times.
Ans. (1) Local time differs by 1 hour for each 15°. (2) If the difference between the longitudinal extent of the country is less than one or two hours, only one time zone is set for the country. (3) But for countries with difference of more than 2 hours, one standard time is not enough and more than 1 time zone is considered. (4) Canada spans almost 90° of longitude. Hence, Canada has 6 different time zones.