TIDES — Cause of the periodic rise and fall of sea level Question: The periodic rise and fall of sea level (tides) on Earth is primarily related to which factor?
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AThe position of the Moon relative to Earth and the gravitational pull exerted mainly by the Moon and partly by the Sun
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BInfrared rays from the Sun heating the oceans
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CUltraviolet rays from the Sun altering water density
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DNone of the above
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EElectromagnetic induction by Earth’s core
Answer
Correct Answer: The position of the Moon relative to Earth and the gravitational pull exerted mainly by the Moon and partly by the Sun
Explanation
Introduction / Context:Tides are long-period waves that travel through the oceans in response to gravitational forces. Understanding their cause is fundamental for navigation, coastal engineering, and environmental planning.
Given Data / Assumptions:
- Two principal tide-generating bodies: the Moon and the Sun.
- Relative positions (syzygy vs quadrature) modulate tidal range.
- Electromagnetic or radiative effects are negligible in directly driving tides.
Concept / Approach:Tidal forces arise from the gradient (difference) in gravitational attraction across Earth’s diameter. The Moon, being closer, exerts the dominant effect, while the Sun contributes a secondary component. Alignment (new and full moon) produces spring tides; right-angle positions (first and third quarter) produce neap tides.
Step-by-Step Solution:Identify relevant force: gravitational attraction and its differential across Earth.Recognize lunar dominance due to proximity; add solar contribution.Conclude that tides reflect the changing geometry of these bodies relative to Earth.
Verification / Alternative check:Observed fortnightly cycles of spring and neap tides correspond to Moon–Sun–Earth geometry, confirming the gravitational explanation.
Why Other Options Are Wrong:Infrared/Ultraviolet rays alter temperature or chemistry but do not generate periodic global sea-level oscillations.None of the above — incorrect because the gravitational mechanism is well established.Electromagnetic induction is unrelated to ocean-basin-scale tidal patterns.
Common Pitfalls:Confusing wind-driven storm surges with astronomical tides. Wind and pressure cause weather-related sea-level changes, not the regular tidal cycle.
Final Answer:The position of the Moon relative to Earth and the gravitational pull exerted mainly by the Moon and partly by the Sun