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GeographyMediumAsked in: NDA · NDA-I 2019, GAT

What is the time gap in occurrence of two successive tides at a given place on the ocean surface ?

  1. A.12 hours
  2. B.12 hours 26 minutes
  3. C.24 hours
  4. D.24 hours 52 minutes

Correct answer

B. 12 hours 26 minutes

Explanation

The correct answer is B, 12 hours 26 minutes. Most places have two high tides a day, and because the moon rises about 52 minutes later each day, each high tide comes about 12 hours 26 minutes after the last.

Tides are caused mainly by the moon's pull on the oceans, helped by the sun. Water bulges on the side facing the moon and on the opposite side, so a place passes through two bulges as the earth turns. But the moon also moves along its orbit, so the earth must turn a little more than once, about 24 hours 52 minutes, to face the moon again. Half of that is the gap between two high tides.

A is wrong because a gap of exactly 12 hours ignores the moon's daily movement. C is wrong because 24 hours would mean only one tide a day at the speed of the sun, which is not the normal pattern. D is wrong because 24 hours 52 minutes is the gap between the moon facing a place twice, which brings two tides, not one.

Exam tip: lunar day 24 hours 52 minutes; two high tides about 12 hours 26 minutes apart.

Practice Questions

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Q2.GeographyAsked in: CDS · CDS-II 2017, GKMedium

Which of the following statements is/are correct? 1. Himalayan rivers have their origin in the snow-covered areas, hence are dry in winter season. 2. Rivers of the Peninsular Plateau have reached maturity. 3. Himalayan rivers depict all the three stages of normal cycle of erosion. Select the correct answer using the code given below.

  1. A.2 only
  2. B.1 and 3 only
  3. C.2 and 3 only
  4. D.1, 2 and 3
Show answer
Correct answer: C. 2 and 3 only

Himalayan rivers are perennial, so statement 1 is wrong, while statements 2 and 3 are correct. Himalayan rivers such as the Ganga, Indus and Brahmaputra rise from glaciers and snowfields and also get monsoon rain, so they flow all year round, including in winter.

Q3.GeographyAsked in: CDS · CDS-II 2017, GKMedium

Which of the following statements related to latitude are true? 1. Rainfall, temperature and vegetation vary with latitude. 2. The difference between the longest day and the shortest day increases with latitude. 3. Indira Point is located approximately at 6°45' N latitude. Select the correct answer using the code given below.

  1. A.1 and 2 only
  2. B.1 and 3 only
  3. C.2 and 3 only
  4. D.1, 2 and 3
Show answer
Correct answer: D. 1, 2 and 3

All three statements about latitude are true. Latitude decides how directly the Sun's rays strike a place, so temperature, rainfall and the type of vegetation change from the equator towards the poles, from hot, wet rainforests to cold tundra.

Q4.GeographyAsked in: CDS · CDS-II 2017, GKMedium

Which of the following lakes is/are situated in Ladakh? 1. Tso Kar 2. Pangong Tso 3. Tsomgo 4. Tso Moriri Select the correct answer using the code given below.

  1. A.1 only
  2. B.2 and 3
  3. C.1, 2 and 4
  4. D.2 and 4 only
Show answer
Correct answer: C. 1, 2 and 4

Tso Kar, Pangong Tso and Tso Moriri are high-altitude lakes of Ladakh, while Tsomgo lies in Sikkim. Pangong Tso, at about 4,350 metres, is a long, narrow lake that stretches from Ladakh into Tibet, and most of its length lies on the Chinese side.