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GeographyMediumAsked in: CDS · CDS-II 2024, GK

Eratosthenes, a Greek philosopher measured the Earth's circumference based on the angle of Sun rays at two different points. Which cities were they ?

  1. A.Alexandria and Syene
  2. B.Syene and Troy
  3. C.Alexandria and Troy
  4. D.Alexandria and Thebes

Correct answer

A. Alexandria and Syene

Explanation

The correct answer is A, Alexandria and Syene. Around 240 BC Eratosthenes, the librarian of Alexandria in Egypt, learnt that at noon on the summer solstice the Sun shone straight down a well at Syene (modern Aswan), so it was directly overhead there. At the same moment in Alexandria, further north, a vertical stick cast a shadow showing the Sun about 7.2 degrees away from the vertical. Since 7.2 degrees is one-fiftieth of a full circle, he multiplied the distance between the two cities by fifty and got a circumference close to the modern value of about 40,000 km. He is also credited with coining the word geography. Option B is wrong because Troy, in present-day Turkey, played no part in the measurement. Option C is wrong for the same reason; only Alexandria is right. Option D is wrong because Thebes (Luxor) was not the second point; Syene, close to the Tropic of Cancer, was chosen for its overhead noon Sun. Exam tip: Eratosthenes, Alexandria and Syene (Aswan), 7.2 degrees, one-fiftieth of a circle.

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.