In a group discussion on shape and size of the Earth, three students stated the following points : 1. Student 1 : The shape of the Earth is basically an oblate spheroid. 2. Student 2 : The polar diameter of the Earth is more than the equatorial diameter. 3. Student 3 : Bulge along the equatorial region is due to revolution of the Earth. Who among the above students is/are correct?
- A.Student 1 only
- B.Student 1 and Student 2 only
- C.Student 2 and Student 3 only
- D.Student 1, Student 2 and Student 3
Correct answer
Explanation
The correct answer is A, Student 1 only. The Earth is an oblate spheroid, slightly flattened at the poles and bulging at the equator, but the bulge comes from its rotation, and its polar diameter is the shorter one. As the Earth spins on its axis, the speed of rotation is greatest at the equator, and the outward effect of this spin pushes material there outwards, making the equator bulge. As a result the equatorial diameter is about 12,756 km and the polar diameter about 12,714 km, a difference of roughly 43 km. Because of the flattening, a person at the poles is slightly closer to the Earth's centre and weighs slightly more than at the equator. Its exact shape, with small irregularities, is also called a geoid. Option B is wrong because Student 2 has it the wrong way round; the polar diameter is shorter. Option C is wrong because Students 2 and 3 are both wrong. Option D is wrong because only Student 1 is right; the bulge is due to rotation, not revolution. Exam tip: rotation causes the equatorial bulge; revolution causes the seasons.
Practice Questions
View allWhich one of the following is not a minor plate ?
- A.Cocos Plate
- B.Nazca Plate
- C.Caroline Plate
- D.Antarctic Plate
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The Antarctic Plate, carrying Antarctica and the ocean around it, is one of the seven major lithospheric plates. Plate tectonics divides the lithosphere into seven major plates and several minor ones.
Read the full explanation →Which of the following statements with reference to shadow zones in an event of an earthquake is/are correct ? 1. Zone between 105° and 145° from epicentre was identified as the shadow zone for both P-waves and S-waves 2. The shadow zone of P-waves is much larger than that of the S-waves Select the answer using the code given below:
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Show answer
The band between 105° and 145° from the epicentre receives neither P-waves nor S-waves, but it is the S-wave shadow zone that is much larger, so statement 2 is wrong.
Read the full explanation →Which of the following statements about Ring of Fire is/are correct ? 1. It is a zone of convergence plate boundaries 2. It is an active seismic and volcanic zone 3. It is associated with deep trench Select the correct answer using the code given below :
- A.1 and 2 only
- B.2 and 3 only
- C.1 only
- D.1, 2 and 3
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The Ring of Fire around the Pacific is a belt of convergent plate boundaries, full of active volcanoes and earthquakes and lined by deep ocean trenches.
Read the full explanation →Which one of the following rivers is not a tributary of river Brahmaputra ?
- A.River Manas
- B.River Kameng
- C.River Mahananda
- D.River Subansiri
Show answer
The Mahananda rises in the Darjeeling hills, flows through north Bengal and Bihar and joins the Ganga, not the Brahmaputra.
Read the full explanation →Which of the following statements regarding tropical cyclones is/are correct ? 1. These storms develop during the summer and autumn in every tropical ocean except the South Atlantic and eastern South Pacific Oceans. 2. Tropical cyclones that occur in the North Atlantic and eastern North Pacific Oceans are known as typhoons. 3. Tropical cyclones that occur in the Indian and South Pacific Oceans are called cyclones. Select the answer using the code given below :
- A.3 only
- B.1 and 2 only
- C.1 and 3 only
- D.1, 2 and 3
Show answer
Tropical cyclones of the North Atlantic and eastern North Pacific are called hurricanes, not typhoons, so statement 2 is wrong.
Read the full explanation →