(a) Distinguish between local time and standard time. (b) The local time of Town A, located on longitude 70°E and latitude 45°N, is 7.46 p.m., calculate the...
Question 1 Report
(a) Distinguish between local time and standard time.
(b) The local time of Town A, located on longitude 70°E and latitude 45°N, is 7.46 p.m., calculate the longitude of Town B on the same latitude when its local time is 5.30 a.m.
Answer Details
(a) Local time versus standard time
| Local time | Standard time |
|---|---|
| Time based on the position of the overhead sun for a particular meridian (longitude). | A single, uniform time adopted for a whole country or time zone. |
| It changes with every degree of longitude (4 minutes per degree). | It is fixed for the whole zone regardless of small changes in longitude. |
| Determined by a chosen central meridian's local time in each zone. | Based on a chosen standard meridian (often a multiple of 15 degrees). |
(b) Longitude of Town B
Latitude is the same, so it does not affect the calculation. Use the difference in local time between the two towns.
Town A (70 degrees E): local time = 7.46 p.m. = 19:46.
Town B: local time = 5.30 a.m. = 05:30.
Time difference:
\[ 19{:}46 - 05{:}30 = 14 \text{ hours } 16 \text{ minutes} \]Convert to minutes: \(14 \times 60 + 16 = 856\) minutes.
Since 1 degree of longitude = 4 minutes of time, the longitude difference is:
\[ \frac{856}{4} = 214^{\circ} \]Town B's local time (05:30) is earlier (behind) Town A's (19:46), so Town B lies to the west of Town A.
Longitude of B = \(70^{\circ}E - 214^{\circ}\).
\[ 70 - 214 = -144^{\circ} \]A negative value means we have crossed the 0 degree meridian into western longitudes:
\[ 144^{\circ}W \]Town B lies on longitude \(144^{\circ}W\).
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