Tides, Waves & Tsunamis – NDA Geography PYQs

NDA 2017-II

Q. 1. Which one of the following has the highest tidal range in the world?

(a) Gulf of Mexico

(b) English Channel

(c) Bay of Fundy

(d) Gulf of Khambhat (Cambay)

Answer: (c) Bay of Fundy

Explanation: The Bay of Fundy, located between the Canadian provinces of New Brunswick and Nova Scotia, has the world’s highest tidal range: reaching up to approximately 16 metres (52 feet) between high and low tide. The extreme tidal range results from a combination of factors: 1. The funnel shape of the bay: as water flows in from the wider ocean into the narrowing bay, it is forced upward. 2. Resonance: the natural resonant frequency of the bay closely matches the tidal period (approximately 12.4 hours), amplifying the tides. The Gulf of Khambhat (Cambay) in India also has a high tidal range: among the highest in the Indian Ocean region. Concept Tested: Bay of Fundy, Canada: world’s highest tidal range (~16 m); funnel shape and resonance amplify tides

NDA 2016-I

Q. 2. Which of the following statements about ocean waves is NOT correct?

(a) Waves are created primarily by the action of wind on the ocean surface

(b) Water particles in waves move forward with the wave

(c) The height of a wave depends partly on the strength and duration of the wind

(d) Waves transfer energy through the ocean

Answer: (b) Water particles in waves move forward with the wave

Explanation: Option (b) is NOT correct: it is false. In ocean surface waves, water particles do NOT move forward with the wave. Instead, they move in circular (or elliptical) orbits: returning close to their original position after the wave passes. It is the wave ENERGY (and the wave FORM) that moves forward: not the water itself. This is why a floating object (like a buoy) bobs up and down as waves pass but does not travel with the wave. (a): Correct. Waves are primarily created by wind friction on the ocean surface. (c): Correct. Wave height increases with wind speed, duration, and fetch (distance over which wind blows). (d): Correct. Waves are a mechanism of energy transfer through the ocean. Concept Tested: Ocean waves: water particles move in CIRCULAR orbits (NOT forward); it is wave energy that moves forward

NDA 2015-I

Q. 3. Consider the following statements about Tsunamis:

1. Tsunamis have very long wavelengths in the open ocean.

2. Tsunamis are caused by submarine earthquakes.

3. Wave height increases as depth of ocean decreases.

Which of the statements given above are correct?

(a) 1 and 2 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) 1, 2 and 3

Answer: (d) 1, 2 and 3

Explanation: Statement 1: Correct. In the open ocean, tsunamis have extremely long wavelengths (100–500 km between crests) and travel at high speeds (~800 km/h). They appear barely noticeable: only about 30 cm high in deep water. Statement 2: Correct. Tsunamis are most commonly triggered by submarine (underwater) earthquakes along subduction zones. They can also be caused by underwater landslides and volcanic eruptions. Statement 3: Correct. As a tsunami approaches shallower coastal water, the wave slows down (wavelength decreases) but its height increases dramatically: from centimetres to metres or tens of metres. This is called shoaling. Concept Tested: Tsunamis: long wavelength in open ocean; caused by submarine earthquakes; height increases as depth decreases (shoaling)

NDA 2013-I

Q. 4. Tides in the ocean are primarily caused by:

(a) Gravitational pull of the Moon

(b) Gravitational pull of the Sun

(c) Rotation of the Earth

(d) Revolution of the Moon

Answer: (a) Gravitational pull of the Moon

Explanation: Tides are primarily caused by the gravitational pull of the Moon on Earth’s oceans. The Moon’s gravity creates a tidal bulge on the side of Earth nearest the Moon, and a corresponding bulge on the opposite side (due to inertia/centrifugal effects). As the Earth rotates, these bulges sweep around the planet: creating the cycle of high and low tides. The Sun also exerts a tidal force but only about 46% as strong as the Moon’s (despite the Sun being much larger, it is much farther away: tidal force depends on the cube of distance). Earth’s rotation determines when tides occur at a given location but is not the primary CAUSE. Concept Tested: Tides primarily caused by Moon’s gravitational pull; Sun contributes but only ~46% as much (too distant)

NDA 2012-II

Q. 5. Neap tides occur when:

(a) The Sun and Moon are on the same side of the Earth

(b) The Moon is nearest to the Earth

(c) The Moon is at right angles to the Earth-Sun line

(d) The Sun and Moon are in line with the Earth

Answer: (c) The Moon is at right angles to the Earth-Sun line

Explanation: Neap tides occur during First Quarter and Last Quarter moon phases, when the Moon is at 90° to the Earth-Sun line. In this configuration: 1. The Sun’s gravitational pull works perpendicular to the Moon’s gravitational pull. 2. The solar and lunar tidal forces partially cancel each other out. 3. The result is a smaller tidal range: high tides are lower than normal, and low tides are higher than normal. Neap tides occur twice a month, approximately seven days after spring tides. Concept Tested: Neap tides: Moon at right angles to Sun-Earth line (quarter moon); gravitational forces cancel; minimum tidal range

NDA 2010-II

Q. 6. Spring tides occur when:

(a) The Moon is at right angles to the Earth-Sun line

(b) The Sun, Moon and Earth are in the same straight line

(c) The Moon is farthest from the Earth

(d) The Moon is nearest to the Earth

Answer: (b) The Sun, Moon and Earth are in the same straight line

Explanation: Spring tides occur during New Moon and Full Moon phases, when the Sun, Earth, and Moon are aligned (in syzygy). During New Moon: Sun and Moon are on the same side of Earth → their gravitational forces add together → highest high tides and lowest low tides (maximum tidal range). During Full Moon: Moon is on the opposite side of Earth from the Sun → they still align → same combined gravitational effect. Spring tides are the most extreme tides: they occur twice a month (every ~14 days). Concept Tested: Spring tides: Sun, Moon, Earth aligned (new/full moon); gravitational forces add; maximum tidal range

★ JOVIK Exam Insight Tidal types for NDA: Spring Tides: Sun + Moon + Earth aligned (new or full moon); maximum tidal range; occur twice a month. Neap Tides: Moon at 90° to Sun-Earth line (quarter moon); Sun and Moon partially cancel each other; minimum tidal range; occur twice a month between spring tides. Tidal range: difference between high and low tide. World’s largest tidal range: Bay of Fundy, Canada (~16 m).

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