Question

Arun called his mother from Digboi at 7 am. At what local time will his mother pick up his call at Jaisalmer?

Answer 1

Sun rises in the east and sets in the west. Thus sun moves from east to west as the earth rotates from west to east. Earth can be seen as a sphere of 360 ̊. Earth rotates this 360 ̊ in 24 hours.

Rotation of earth in 1 hour = 360/24 = 15 ̊

Arun calls from Digboi, Assam at 7.00 AM. The longitudinal coordinates that determine the time of Brasilia are 95.63 ̊ E. Jaisalmer is at the longitudinal time zone coordinate of 70.9 ̊ E.

The difference in longitude between Brasilia and New Delhi = 95.63 ̊ E – 70.9 ̊ E

= 24.73 ̊ E

Difference in time = 24.73/15 = 1.64 hours

= 1 hour + (0.64*60) minutes

= 1 hour + 38 minutes (approx.)

Since the earth rotates from west to east, time zone at 70.9 ̊ E will be ahead of 95.63 ̊ E. Thus when the time would be ahead in Jaisalmer by 1 hour 38 minutes. But since India is following a standard time at the longitudinal coordinate 82.5 ̊ E, the whole country will have the same time zone that is 5 hours 30 minutes ahead of the Greenwich Time. Thus the local time at Jaisalmer would be 7 AM.