In physical geography, tides in the sea are primarily caused by which of the following gravitational effects?

Introduction / Context:
Tides are regular rise and fall of sea level that occur along coastlines throughout the world. Understanding what causes tides is a basic part of physical geography and earth science. Most exam questions on this topic test whether students know that tides result from gravitational attraction mainly of the Moon and also of the Sun, together with the rotation of the Earth, rather than from a single body acting alone.

Given Data / Assumptions:

• The question asks what causes tides in the sea.
• The options include gravity of Earth and Sun, effect of Sun, combined effect of Moon and Sun, and effect of Moon.
• We assume standard textbook explanations that highlight both the Moon and the Sun as gravitational sources.
• The correct option should reflect the joint influence that creates the observed tidal patterns.

Concept / Approach:
The key concept is that tides are created by differential gravitational forces, called tidal forces, produced by both the Moon and the Sun acting on the Earth's oceans. The Moon has the stronger tidal effect because it is much closer to Earth, but the Sun also contributes significantly. When the gravitational pulls of the Moon and Sun align, spring tides occur; when they act at right angles, neap tides occur. Therefore, the accurate description among the options is the combined effect of Moon and Sun, not only one or the other.

Step-by-Step Solution:
Step 1: Recall that the Moon exerts a gravitational pull on Earth that is strong enough to cause a bulge in the ocean on the side facing the Moon and another bulge on the opposite side.Step 2: Remember that the Sun also exerts gravity on Earth, which modifies the height of tides produced by the Moon.Step 3: Note that when Sun, Moon, and Earth are aligned (during full and new moon), their combined gravitational effect produces higher spring tides.Step 4: Recognise that when the Sun and Moon are at right angles relative to Earth, their tidal effects partially cancel, leading to lower neap tides.Step 5: Therefore, the correct conceptual description is that tides result from the combined effect of the Moon and the Sun.

Verification / Alternative check:
Textbook diagrams of tides almost always show both the Moon and the Sun around the Earth, with arrows indicating gravitational pull. They also explain that the tidal range varies with lunar phases because the Sun sometimes reinforces and sometimes reduces the Moon's tidal influence. If only the Moon or only the Sun were responsible, these variations in spring and neap tides could not be explained in the standard way. This reinforces that the combined effect of Moon and Sun is the most accurate option provided.

Why Other Options Are Wrong:
Gravitational force of Earth and Sun: The Earth's own gravity holds the oceans in place; it does not create the tidal bulges in the sense described here, and leaving out the Moon makes the statement incomplete.
Effect of Sun: The Sun does influence tides, but the Moon has a stronger tidal effect and cannot be ignored, so this option is not fully correct.
Effect of Moon: The Moon is the dominant cause of tides, but the Sun also modifies tidal range, so a statement that mentions only the Moon is not fully accurate.

Common Pitfalls:
Some learners think only the Moon matters and pick the option that mentions the Moon alone. Others are misled by the enormous mass of the Sun and choose options that emphasise the Sun, forgetting that tidal force depends strongly on distance as well as mass. The safest approach is to remember that both Moon and Sun play roles, with the Moon being stronger, so the phrase "combined effect of Moon and Sun" best captures the full explanation for tides in the sea.

Final Answer:
Tides in the sea are mainly produced by the combined effect of the gravitational pulls of the Moon and the Sun acting on Earth's oceans.