Question

How much of a time period $15{}^\circ $ of longitudes account for?
A. 4min
B. 15min
C. 30min
D. 60min

Answer 1

Hint: As a first step, you could understand all the given terms like longitude and accounted time period. Then you could recall what the known time difference for one degree longitude is. Then you could multiply that value with 15 to get the required answer. Remember, though longitudes are imaginary, they have great significance.

Complete Answer:In the question, we are asked to find the time period accounted for by $15{}^\circ $ of longitudes.
Firstly, let us understand what exactly these longitudes are. They can be defined as the measurement of angular distance of a place east or west of the prime meridian. Meridians are actually the imaginary lines that run around the earth vertically from north pole to south pole. We know that each meridian measures one arc degree of longitude and we also know that the distance around the earth is$360{}^\circ $.
We should firstly know the time difference between each longitude or$1{}^\circ $ longitude in order to find the time period accounted for by $15{}^\circ $ longitude.
The time difference between each longitude is found to 4 minutes. That is,
$1{}^\circ \to 4\min $
$\Rightarrow 15{}^\circ \to 15\times 4\min $
$\therefore 15{}^\circ \to 60\min $
Therefore, multiplying the time difference of $1{}^\circ $ longitude with 15 we get the time period accounted for by $15{}^\circ $ longitude as 60minutes.
Hence, option D is found to be the correct answer.

Note: The prime meridian passing through Greenwich, London is taken as the 0 degree longitude. The time here taken as the standard time and all other time zones are calculated with respect to this. We know that one degree longitude accounts for a time period of 4minutes. This means that when the time at the prime meridian (Greenwich$0{}^\circ $) is 12.00am it would be 12.04am at one degree meridian.