Waves and tides

The correct answer is B. A spit grows as longshore drift deposits sediment along the coast. Near its tip, a change in wind or wave direction can change the direction in which sediment is carried and deposited, bending the tip into a curve. Tides do not need to stop, and glacial pressure and karst solution are unrelated processes.

A is correct. Wave refraction bends wave fronts around an island, often leaving a relatively sheltered zone behind it. Sediment carried into this lower-energy area can be deposited and may gradually form a ridge linking the island to the mainland—a tombolo.

A is correct. Waves cut a platform at the base of a sea cliff. As the cliff retreats inland, an older part of the platform may remain behind. If relative sea level falls or the land rises, that relict platform may stand above the present shoreline, recording an earlier coastal position.

The governing concept is the distinction between oscillatory wave motion and directed water transport. In a surface wave, energy travels through the water while individual water particles commonly move in orbital or oscillatory paths and may show limited net forward movement. An ocean current is a more sustained, organized movement of a water mass from one region toward another. Currents can be driven by wind, density differences, pressure gradients, and Earth’s rotation. A wave is not necessarily a river, a current is not a cloud, and the two processes are not identical. Thus option A gives the simplest accurate difference, while acknowledging that real waves and currents can interact.

The governing concept is the difference in cause and time pattern. Tides are predictable, large-scale changes in sea level produced mainly by the gravitational effects of the Moon and Sun together with Earth’s rotation and basin shape. A tsunami is a series of long waves generated when a large volume of seawater is suddenly displaced, commonly by an undersea earthquake, but also sometimes by a submarine landslide, volcanic eruption, or other disturbance. Thus tides are regular astronomical phenomena, whereas tsunamis are sudden hazards that may travel across an ocean and grow near coasts. Option A is correct; the other choices incorrectly make the two identical or assign each phenomenon an exclusive cause.

The governing concept is temporal measurement in wave motion. Wave period is the time required for one complete cycle to pass a fixed observation point. In practice, an observer can measure the interval between the passage of two successive crests or two successive troughs. If a crest passes at 10:00:00 and the next crest passes at 10:00:08, the wave period is 8 seconds. Period is commonly represented by T and is related to frequency by T = 1/f. It is different from wavelength, which is a distance, and from wave height, which measures vertical size. Therefore, option A is correct.

The governing concept is the difference between horizontal spacing and vertical size in a wave. Wavelength is the horizontal distance between corresponding points on successive cycles, such as crest to crest or trough to trough. Wave height is the vertical distance from a crest to the neighboring trough. For example, if successive crests are 12 metres apart, the wavelength is 12 metres; if the crest is 2 metres above the trough, the wave height is 2 metres. Wavelength is commonly denoted by λ, whereas height describes amplitude-related size and is not the length of the coast. Therefore, option A is correct.

Wave growth is governed by three important wind controls: wind speed, duration, and fetch. Stronger wind transfers energy more rapidly; a longer duration allows repeated energy transfer; and a larger open-water distance gives the wind more space over which to act. When all three factors are high, waves generally become higher, longer, and more energetic, although actual size is also limited by depth, storms, and other conditions. Therefore option A is correct. The other options are impossible or unrelated: wind does not always eliminate waves, it does not stop astronomical tides, and it cannot instantly dry the sea. The question asks for the general, not absolute, effect.

Fetch is a technical term in wave geography and oceanography. It means the uninterrupted distance across open water over which wind blows in a fairly consistent direction and transfers energy to the sea surface. A longer fetch generally gives waves more opportunity to grow, especially when wind speed and duration are also sufficient. Therefore option B is correct. Option A describes wave height, the vertical distance from trough to crest, not fetch. Option C refers to the level or range of a tide, which is controlled mainly by gravitational forces. Option D is a property of seawater and has no meaning as the wind distance used in wave formation.

The governing concept is wave energy transfer. In an ordinary surface wave, individual water particles usually move in small orbital or oscillatory paths rather than travelling forward with the wave over a long distance. The disturbance and its energy, however, propagate from one place to another. This distinction makes option B correct: particles mainly oscillate while energy moves forward. Option A reverses both ideas because particles do not normally flow permanently far and energy is not stationary. Options C and D describe processes that are not the physical behaviour of ordinary waves. In shallow or breaking water, particle motion can become more complex, but the basic distinction remains valid.

Wavelength and wave period are different measurements of a wave. Wavelength, usually represented by the symbol lambda, is a spatial distance: it is the distance between corresponding points on successive waves, such as crest to crest or trough to trough. Wave period, usually represented by T, is a time interval: it is the time taken for one complete wave cycle or for successive crests to pass a fixed point. Thus option A is correct. Wave height is a separate vertical measurement. Salinity is a property of seawater, and neither wavelength nor period is a name for a tide. Their relationship may be written as wave speed = wavelength divided by period.

The governing concept is the transformation of waves as water depth decreases. In deep water, the lower part of a wave is less affected by the seabed. As the wave enters shallow water, interaction with the bottom increases and friction slows the lower portion. The crest continues moving relatively faster, the wave becomes steeper and less stable, and it eventually collapses or breaks when its shape can no longer be maintained. Therefore option C is correct. The water does not need to change colour, the Moon’s gravity does not suddenly end, and a breaking wave still contains energy; that energy is released through turbulence, spray, and sediment movement.

Tidal range is the difference in water level between high tide and low tide. During a spring tide, which occurs near the new moon and full moon, the Sun, Moon, and Earth are approximately aligned. The gravitational tide-producing effects of the Sun and Moon then act along nearly the same line and reinforce one another. This produces higher high tides, lower low tides, and consequently a larger tidal range. Therefore option B is correct. Wind may alter local water levels temporarily but is not the defining cause of a spring tide. River inflow and sea temperature do not create the astronomical alignment responsible for this increased range.

Neap tide is produced around the first-quarter and third-quarter phases of the Moon. At these times, the Sun, Earth, and Moon are positioned approximately at a right angle. The solar and lunar tidal forces therefore act in different directions instead of reinforcing one another along the same line. Their combined effect produces a smaller difference between high-water and low-water levels, so the tidal range is reduced. Option A is correct because it identifies both the quarter phases and the geometrical reason. Option B is false because the sea still contains water, option C confuses ordinary wind waves with gravitational tides, and option D is false because the Moon has not moved extremely far away.

A spring tide occurs when the gravitational effects of the Sun and Moon reinforce each other. At new moon, the Moon lies approximately between the Sun and Earth; at full moon, the Earth lies approximately between the Sun and Moon. In both arrangements, the three bodies are nearly aligned, although the order is different. The solar and lunar tidal forces then act along nearly the same line, producing higher high tides, lower low tides, and a larger tidal range. Option A is correct. Wind, the presence of waves, and whether the sea dries are not the governing causes, so options B, C, and D are incorrect.

The first-quarter and third-quarter phases place the Sun and Moon approximately at right angles as viewed from Earth. Because tidal forces depend on the relative positions of these bodies, their effects do not combine directly along one line during these phases. The solar contribution partly offsets the lunar contribution in determining the total tidal bulge. Consequently, high tides are not as high, low tides are not as low, and the tidal range becomes smaller than during a spring tide. Option A states the controlling astronomical relationship. Options B, C, and D are incorrect because the Sun and Moon do not disappear, wind is not the primary cause of astronomical tides, and salinity does not become zero.

The Moon produces the stronger apparent tidal effect mainly because it is much closer to Earth. Tides are caused not simply by the total gravitational pull but by the difference in gravitational attraction between the near and far sides of Earth. This tidal, or differential, effect decreases very rapidly with distance, approximately following an inverse-cube relationship, whereas ordinary gravitational attraction follows an inverse-square relationship. The Sun is vastly more massive and also contributes to tides, but its enormous distance makes its differential effect weaker than the Moon's. Option A is therefore correct. The other options deny solar gravity, invent a composition-based cause, or incorrectly say the Sun stops tides.

A tidal current is the horizontal movement of seawater associated with the regular rise and fall of the tide. When tidal forces raise the water level in one area, water flows toward connected coastal or oceanic areas; as the tide falls, the flow reverses or moves seaward. In narrow estuaries, bays, channels, and inlets, this movement can become especially noticeable and strong. Option B is correct because it identifies both the changing water level and the resulting horizontal flow. A wave's sound has no controlling role, and sea colour or coastal sand alone cannot generate a periodic current. Therefore options A, C, and D are scientifically unsuitable.

Tidal range is the difference in water level between high tide and low tide. This difference matters greatly in ports because a rising tide can increase the depth over a channel, bar, sandbank, or harbour entrance. A vessel with a deep draft may be unable to enter safely at low tide but may enter during high tide when sufficient clearance is available. Port authorities therefore consider tide tables when scheduling arrivals, departures, dredging, and cargo operations. Option A is correct because it links tidal range with navigable water depth. The other options concern unrelated features: tides do not measure mountain height, determine cloud number, or convert seawater into soil.

Ordinary surface waves are mainly generated when wind transfers energy to the sea surface. Their size depends on factors such as wind speed, duration, and the distance over which the wind blows. Tides, in contrast, are broad and regular changes in sea level caused primarily by the gravitational effects of the Moon and the Sun, together with Earth–Moon motion. Some unusual waves, such as tsunami waves, have other causes, but that does not change the standard comparison asked here. Option A is correct because it states the principal causes of ordinary waves and tides. Options B, C, and D incorrectly reverse or oversimplify those causes.

Coastal waves continuously transfer energy to beaches, cliffs, shore platforms, and nearshore sediments. Where wave attack is strong, hydraulic pressure, abrasion, and the impact of moving sediment can wear away rock and soil, producing coastal erosion. When wave energy decreases, especially in sheltered bays or along gently sloping shores, the transported sand and gravel may settle and accumulate, producing deposition. Thus the same broad coastal system can remove material from one place and deposit it in another. Option A is correct because erosion and deposition are the two major geomorphic results. Forest growth, farming, clouds, eclipses, and seasons are not direct works of wave energy.

When waves reach a beach obliquely, their swash carries sand and small particles up the beach at an angle. Gravity then pulls the backwash more directly downslope toward the sea. Repetition of this angled swash and downslope backwash produces a zigzag movement of sediment, with a net transport parallel to the shoreline. This process is commonly called longshore drift or littoral drift and can redistribute beach material over considerable distances. Option A is correct because it identifies movement along the coast. Sediment does not normally vaporise, travel to the Moon, or lose its connection with the sea merely because waves arrive at an angle, so B, C, and D are false.

The governing concept is the geomorphic work of waves. When waves strike a coast, their energy can loosen and remove rock, sand, or soil; this process is coastal erosion. The removed material may be transported along the shore or moved offshore and later deposited where wave energy becomes weaker. Erosion can form cliffs, caves, arches, and wave-cut platforms, while deposition can build beaches, spits, and bars. Therefore, option A is correct because it includes both major processes by which wave action reshapes a coastline. Option B describes no landform-forming mechanism, and options C and D confuse tides, gravity, or wind conditions with the direct erosional and depositional work of waves.

The governing concept is the practical importance of tidal range for navigation. A high tide raises the water level and increases depth over shallow bars, channels, or harbour entrances. This can give vessels with a deep draught enough clearance to enter or leave a port, while a low tide may restrict movement or expose hazards. Port authorities therefore use tide tables to plan safe arrival, departure, and loading operations. Option A is correct because it states the direct relationship between changing sea level and ship movement. Options B, C, and D are physically meaningless: tides do not transport ships onto mountains, remove wind, or freeze seawater. The exact benefit depends on local coastal conditions.

The governing concept is tidal energy as a renewable form of ocean energy. Tides produce a predictable, repeated movement of water because the Moon’s and Sun’s gravitational effects act on Earth’s oceans. A tidal barrage can generate electricity from the difference in water level between high and low tide, while tidal-stream turbines can use the movement of flowing tidal water. The essential natural property is therefore regularity and sufficient water movement, making option A correct. Predictability also distinguishes tidal energy from some weather-dependent sources. Sea colour, sounds made by organisms, and human language do not provide a reliable physical source of mechanical energy, so options B, C, and D are irrelevant distractors.