UPSC Prelims 2015 · Question 70 of 98
UPSC Prelims 2015 question on Causes of Ocean Tides
- ExamUPSC CSE
- Year2015
- PaperGeneral Studies Paper I
- SubjectGeography
- TopicOceanography
- DifficultyEasy
- TypeStatement
Tides occur in the oceans and seas due to which among the following?
1. Gravitational force of the Sun
2. Gravitational force of the Moon
3. Centrifugal force of the Earth
Select the correct answer using the code given below.
Show answer
Answer: D. 1, 2 and 3
Verdict
The answer is 1, 2 and 3. Tides result from the gravitational pull of the Sun and the Moon together with the centrifugal force of the Earth.
Analysis
Statement 2 is CORRECT and the effect is the largest, because the Moon's proximity outweighs its smaller mass. Statement 1 is CORRECT. The Sun's pull is roughly half as strong in tidal terms and its alignment with the Moon produces spring and neap tides. Statement 3 is CORRECT. The centrifugal force arising from the rotation of the Earth and Moon about their common centre of mass counterbalances gravity and explains the second tidal bulge on the side of the Earth facing away from the Moon.
Source
NCERT Class XI, Fundamentals of Physical Geography, page 121.
How to crack it
The single fact that unlocks this topic is the existence of two bulges, one facing the Moon and one facing away. Gravity alone explains only the near bulge, so a second force is logically required, and that is the centrifugal component. Reasoning from the observed pattern to the necessary cause is more reliable than recalling a list. It also sets you up for spring and neap tides, which follow directly from whether the Sun reinforces or opposes the Moon.