Correct Option: B. Monday
Detailed Explanation:
- Understanding the International Date Line (IDL):
- The International Date Line is an imaginary line located at approximately 180 degrees longitude, opposite the Prime Meridian. It serves as the boundary for calendar days.
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When you cross the IDL from west to east (for example, from America to Asia), you subtract a day. Conversely, if you cross from east to west, you add a day.
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Scenario Analysis:
- In this scenario, the traveller is crossing the IDL from America (which is to the east of the IDL) to Asia (which is to the west of the IDL).
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The traveller departs at 12 midnight on Sunday in America.
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Changing the Watch:
- Since the traveller is moving from America to Asia, they are crossing the IDL from west to east. This means they need to add a day to their current time.
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Therefore, when the traveller changes their watch after crossing the IDL, they will move from 12 midnight on Sunday to 12 midnight on Monday.
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Conclusion:
- The correct answer is B. Monday because crossing the IDL in this direction requires the traveller to advance their calendar by one day.
Why Other Options Are Incorrect:
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A. Sunday: This option suggests that the traveller would remain on the same day. However, crossing the IDL means a change in the calendar day, so this option is incorrect.
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C. Tuesday: This option implies that the traveller would skip a day and move two days ahead. This is not how the IDL functions; the traveller only adds one day when crossing from America to Asia.
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D. Saturday: This option suggests that the traveller would go back a day, which is incorrect. The IDL does not cause a backward shift in days when crossing from America to Asia.
Common Pitfalls:
- Confusing the direction of crossing the IDL: Remember that crossing from west to east subtracts a day, while crossing from east to west adds a day.
- Misunderstanding the concept of time zones: The IDL is not a time zone but a date boundary, so it affects the calendar day rather than the hour directly.
Revision Summary:
- The International Date Line separates calendar days; crossing it changes the date.
- Crossing from America to Asia (west to east) means adding a day.
- A traveller at 12 midnight on Sunday in America will change their watch to 12 midnight on Monday after crossing the IDL.
- Always remember the direction of crossing to determine whether to add or subtract a day.