MPSC 2022 Prelims Paper-I · Question 15 of 100

Correct — option (1). Both statements are sound, and they belong together as a problem and its remedy. Statement (A) says that every longitude has a different local time because the earth rotates. Local time is time reckoned from the sun as it is seen at a particular place: noon is the moment the sun crosses that place's meridian. Since the earth turns on its axis from west to east through three hundred and sixty degrees in twenty-four hours, it turns through fifteen degrees in an hour and through one degree in four minutes, so the sun reaches the meridian of a place four minutes later for every degree of longitude further west. Two places on different meridians therefore keep different local times, and the difference is exactly four minutes for each degree between them; a place forty-five degrees east of another has its noon three hours earlier. Statement (B) says that the standard time system is used to remove the difference in local time, and that is what standard time is for. If every town kept its own local time, timetables, telegraphy, administration and broadcasting within a single country would be unworkable, so a country adopts the local time of one chosen meridian and applies it uniformly across its territory. India has adopted the meridian of eighty-two degrees thirty minutes east, which passes near Mirzapur in Uttar Pradesh, and Indian Standard Time is five hours and thirty minutes ahead of Greenwich; the whole country from Gujarat to Arunachal Pradesh uses it, although the local time at the two ends of the country differs by about two hours. Standard time does not abolish local time as an astronomical fact; it replaces it for civil purposes, which is precisely what the statement claims. Both statements being correct, option (1) is the answer.

• (2)Statement (A) is correct but statement (B) is wrong — This option accepts the first statement and rejects the second, and the doubt behind it is usually about the word remove. A candidate reasons that the difference in local time is astronomical, that it goes on existing whatever clocks people agree to use, and that standard time therefore removes nothing. The reasoning is sound as far as it goes but it misreads the claim. Statement (B) is about the practical difference — the difference between the clocks in use at different places within a country — and that difference is exactly what a common standard meridian removes, since every clock in India shows the same reading at the same instant. The habit worth building is to read a statement for what it asserts rather than for the strictest possible sense its words could bear, because an examiner writing a two-sentence assertion pair is describing a system, not drafting a definition.
• (3)Statement (A) is wrong but statement (B) is correct — This option rejects the first statement, and to do so it must deny either that local time varies with longitude or that the earth's rotation is the cause. Neither denial can be sustained. The variation is arithmetically fixed: fifteen degrees of longitude to an hour, one degree to four minutes, so no two meridians can share a local time. As for the cause, candidates sometimes attribute the difference to the earth's revolution around the sun rather than to its rotation on its axis, and the two must be kept apart — the revolution, together with the tilt of the axis, gives the seasons and the varying length of the day through the year, while the rotation gives the daily cycle and with it the succession of local noons from east to west. Statement (A) attributes the difference to the rotation, and that is the right cause.
• (4)Statements (A) and (B) both are wrong — This option rejects both statements and can be dismissed by the same reasoning that establishes each of them. It is chosen mainly by candidates who cannot decide between the middle two options and take the fourth as a way out. That is worth naming as a habit, because an assertion pair of this form always offers exactly four rows — both true, the first only, the second only, neither — and the fourth is printed whether or not it is the answer, so its presence carries no information. The disciplined procedure is to judge Statement (A) on its own and mark it, then judge Statement (B) on its own and mark it, and only then to look for the row that matches the two marks. Here both marks are ticks, and the row that records them is the first one.

The earth turns on its axis once in about twenty-four hours, and every question about time on the globe follows from that single fact and its arithmetic: three hundred and sixty degrees in twenty-four hours is fifteen degrees an hour, one degree in four minutes and one minute of arc in four seconds of time. Local time is what this gives directly — the time shown by the sun at a particular meridian — and it changes continuously as one moves east or west, so it is useless as a common standard. The remedy is to choose one meridian, take its local time and impose it over a wide area, which is standard time. The system is anchored on the prime meridian through Greenwich, from which the world's time zones are counted, and standard meridians are ordinarily chosen as multiples of fifteen degrees, or of seven and a half degrees where a half-hour offset is wanted. India uses eighty-two degrees thirty minutes east, giving a whole-country offset of five and a half hours from Greenwich, and it keeps a single time zone although its territory stretches from about sixty-eight to about ninety-seven degrees east, which is why the sun rises in Arunachal Pradesh roughly two hours before it rises in Gujarat. Large countries such as Russia, the United States and Canada take the opposite course and use several zones. The International Date Line, drawn approximately along the one hundred and eightieth meridian with deviations to avoid dividing island groups and territories, is where the date changes.

This is an assertion pair, printed in this paper as Statement (A) and Statement (B) with upper-case labels — the only question in the whole paper that labels its statements that way, since every other labelled question uses lower-case (a) to (d). The four options are the standard set for the format, and three of them turn on the words wrong or chuk with nothing in the printing to emphasise the negation, so the reader must supply the care. The format is a favourite of MPSC because it can pair a fact with its explanation and test whether a candidate holds both. The technique is invariable: decide each statement separately, mark it, and then read off the row. What makes this particular item instructive is the temptation to over-read Statement (B). Candidates who know a topic well often reject a simply worded statement because it is not stated with the precision they would use themselves, and in a paper that deducts a quarter of the marks for a wrong answer that instinct is expensive. A statement should be judged false only when it asserts something that is not so, not when it is less exact than a textbook would be.

• The earth rotates through three hundred and sixty degrees in twenty-four hours, so it turns fifteen degrees in an hour and one degree in four minutes, and local time changes by four minutes for every degree of longitude.
• Local time is reckoned from the sun at a particular meridian, noon being the moment the sun crosses it, so no two meridians can keep the same local time.
• Standard time is the local time of one chosen meridian applied uniformly over a country or zone, adopted so that clocks within that area agree for civil, administrative and transport purposes.
• Indian Standard Time is based on the meridian of eighty-two degrees thirty minutes east, which passes near Mirzapur in Uttar Pradesh, and is five hours and thirty minutes ahead of Greenwich Mean Time.
• India keeps a single time zone although it extends roughly from sixty-eight to ninety-seven degrees east, so that sunrise in the far east of the country comes about two hours before sunrise in the far west.

• Rejecting a plainly worded statement because it is less precise than a textbook definition, when the test is whether it asserts something untrue
• Attributing the difference in local time to the earth's revolution around the sun instead of to its rotation on its axis
• Choosing the row that rejects both statements as a way of escaping a decision, when that row is printed in every assertion pair regardless of the facts
• Forgetting that this is the one question in the paper labelled with upper-case Statement (A) and Statement (B), and misreading the labels as option letters

Time and longitude reach MPSC papers in three forms: the calculation question, which gives the longitude of two places and asks for the difference in their local times; the fact question, which asks for the standard meridian of India, the offset of Indian Standard Time or the place the meridian passes through; and the assertion pair used here, which tests whether the candidate can connect the rotation of the earth to the need for a standard time. The Commission also sets the International Date Line as a separate item, usually asking why it deviates from the one hundred and eightieth meridian. The arithmetic is the part worth drilling, because fifteen degrees to the hour and four minutes to the degree answers every calculation variant, and it takes only a minute to verify in the examination hall.

No directly related past PYQ was found.

• practice — not a real PYQ

  If the local time at a place on 90 degrees east longitude is 12 noon, what will be the local time at a place on 75 degrees east longitude ?

  • (a)11 a.m.
  • (b)1 p.m.
  • (c)11.30 a.m.
  • (d)12.30 p.m.

  Answer(a) 11 a.m. — the two meridians are fifteen degrees apart, and since the earth turns fifteen degrees in an hour, their local times differ by exactly one hour. The place further west has its noon later, so its clock reads one hour behind: at four minutes to the degree, fifteen degrees gives sixty minutes, and the answer is eleven in the morning.

• practice — not a real PYQ

  The standard meridian of India passes through which of the following ?

  • (a)Ahmedabad in Gujarat
  • (b)Mirzapur in Uttar Pradesh
  • (c)Nagpur in Maharashtra
  • (d)Bhubaneswar in Odisha

  Answer(b) Mirzapur in Uttar Pradesh — the meridian of eighty-two degrees thirty minutes east passes near Mirzapur, and Indian Standard Time is the local time of that meridian, five hours and thirty minutes ahead of Greenwich. The half-hour offset follows from choosing a meridian at a multiple of seven and a half degrees rather than of fifteen, which is how several countries obtain a half-hour zone.