CBSE Class 11 Geography Chapter 14: Movements of Ocean Water - NCERT Solutions

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NCERT Solutions PDF Class 11 PDF

This chapter, "Movements of Ocean Water," delves into the dynamic processes shaping our oceans. It covers the fundamental concepts of waves, explaining their origin and energy sources, primarily wind. The solutions meticulously detail the phenomenon of tides, including their causes (gravitational pull of the moon and sun, centrifugal force) and types like spring tides. It also touches upon the significant impact of ocean currents on global temperatures and climate, particularly highlighting their influence on coastal regions like Northwestern Europe. Understanding these movements is crucial for comprehending oceanography and its effects on weather patterns and navigation. These NCERT Solutions provide clear, step-by-step explanations to help students grasp these complex topics effectively for their exams.

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BoardCBSE
ClassClass 11
SubjectGeography
Session2026
LanguageEnglish
TypeNCERT Solutions
Chapter14. Movements of Ocean Water

Chapter summary

Chapter 14, "Movements of Ocean Water," focuses on the primary ways ocean water moves: waves and tides. The NCERT Solutions explain what waves are, how they are formed by wind, and the factors influencing their size. It also elaborates on tides, their causes due to celestial bodies' gravitational forces, and the conditions leading to spring tides. The chapter further discusses the impact of ocean currents on climate and navigation, offering specific examples. These solutions are designed to clarify these essential oceanographic concepts for Class 11 Geography students.

Learning outcomes

  • Understand the definition and formation of ocean waves.
  • Identify the primary energy source for ocean waves.
  • Define tides and explain the celestial forces causing them.
  • Differentiate between various tidal phenomena like spring tides.
  • Analyze the influence of ocean currents on global temperatures and climate.
  • Recognize the practical applications of ocean movements in navigation.

Topics covered

Paper topics

  • Ocean Waves
  • Wave Energy
  • Factors affecting wave size
  • Tides
  • Causes of Tides
  • Gravitational Pull
  • Centrifugal Force
  • Spring Tides
  • Ocean Currents
  • Effect of Currents on Temperature
  • Currents and Climate
  • Navigation and Tides

Important topics

  • Causes and types of Tides
  • Formation and energy of Waves
  • Influence of Ocean Currents on Climate
  • Astronomical terms related to orbits (Perigee, Apogee)

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Questions and Solutions

Multiple choice question

1. Upward and downward movement of ocean water is known as the:
  1. tide
  2. current
  3. wave
  4. none of the above
Solution: The alternate rise and fall of the ocean water level is a phenomenon known as a tide. Waves are oscillatory movements on the surface, and currents are continuous horizontal movements of water. Therefore, the correct answer is (a) tide.

Multiple choice question

2. Spring tides are caused:
  1. As result of the moon and the sun pulling the earth gravitationally in the same direction.
  2. As result of the moon and the sun pulling the earth gravitationally in the opposite direction.
  3. Indention in the coast line.
  4. None of the above.
Solution: Spring tides occur when the Sun, the Moon, and the Earth are aligned in a straight line. During this alignment, the gravitational pulls of both the Sun and the Moon combine to create exceptionally high high tides and very low low tides. This happens during the new moon and full moon phases when the Moon and the Sun are pulling the Earth in the same direction. Therefore, the correct answer is (a).

Multiple choice question

3. The distance between the earth and the moon is minimum when the moon is in:
  1. Aphelion
  2. Perigee
  3. Perihelion
  4. Apogee
Solution: The terms related to the Earth-Moon distance are perigee and apogee. Perigee is the point in the Moon's orbit where it is closest to the Earth, and apogee is where it is farthest. Aphelion and perihelion refer to the Earth's distance from the Sun. Since the question asks about the Earth-Moon distance, the minimum distance occurs at perigee. Therefore, the correct answer is (b) Perigee.

Multiple choice question

4. The earth reaches its perihelion in:
  1. October
  2. September
  3. July
  4. January
Solution: Perihelion is the point in Earth's orbit where it is closest to the Sun. This event typically occurs in early January each year. Aphelion, when Earth is farthest from the Sun, occurs in early July. Therefore, the correct answer is (d) January.

Answer the following questions in about 30 words

(i) What are waves?
Solution: Ocean waves are the visible, oscillatory movements on the surface of the sea, characterized by the alternate rising (crest) and falling (trough) of the water. They are essentially the transfer of energy through the water, often caused by wind.

Answer the following questions in about 30 words

(ii) Where do waves in the ocean get their energy from?
Solution: Waves in the ocean primarily get their energy from the wind. As wind blows across the water surface, it transfers energy, causing the water to move and form waves. The size and force of these waves depend significantly on the wind's velocity, the duration for which it blows, and the distance over which it can travel unobstructed (fetch).

Answer the following questions in about 30 words

(iii) What are tides?
Solution: Tides are the periodic and predictable rise and fall of the sea level that occurs on most coastlines around the world, typically once or twice a day. They are primarily caused by the gravitational forces exerted by the Moon and, to a lesser extent, the Sun.

Answer the following questions in about 30 words

(iv) How are tides caused?
Solution: Tides are primarily caused by the differential gravitational pull of the Moon and the Sun on the Earth's oceans. The Moon's gravity pulls the water towards it, creating a bulge on the side facing the Moon. A similar, though smaller, bulge occurs on the opposite side due to the centrifugal force acting against gravity. The Sun's gravity also influences tides, especially during new and full moons.

Answer the following questions in about 30 words

(v) How are tides related to navigation?
Solution: Tides play a crucial role in navigation by influencing water depth in coastal areas and estuaries. Higher tides can allow larger ships to access shallower ports or navigate further up rivers. For example, the Port of Kolkata, located far inland, remains accessible to ocean-going vessels due to the significant tidal range in the Hooghly River.

Answer the following questions in about 150 words

1. How do currents affect the temperature? How does it affect the temperature of coastal areas in the N. W. Europe?
Solution: Ocean currents have a profound impact on global temperatures and climate. Currents originating from tropical regions carry warm water towards the poles, moderating temperatures in higher latitudes. Conversely, currents originating from polar regions transport cold water towards the equator, cooling the areas they pass through. In the case of Northwestern Europe, the North Atlantic Drift, a warm current, significantly influences its climate. This warm current brings warmer water from the tropics, raising the air temperature above it. As a result, coastal areas in Northwestern Europe experience a much milder and more temperate climate than other regions at similar latitudes, preventing them from freezing during winter and contributing to a distinct marine climate. Without this warm current, the region would experience much harsher, colder winters.

Common mistakes

  • Confusing the terms aphelion/perihelion with apogee/perigee.
  • Misunderstanding the direction of gravitational forces during spring tides.
  • Not clearly linking wind characteristics to wave energy.
  • Incomplete explanation of the combined effect of gravity and centrifugal force on tides.

Revision tips

  • Draw diagrams to illustrate the positions of the Earth, Moon, and Sun during spring and neap tides.
  • Create a table summarizing the causes and effects of waves, tides, and currents.
  • Focus on understanding the relationship between ocean currents and climate patterns, especially for coastal regions.
  • Review the definitions of astronomical terms like perigee and apogee in relation to Earth-Moon distance.

Practice MCQs

Q1. What is the term for the alternate rise and fall of the ocean surface?

Q2. Which celestial phenomenon causes spring tides?

Q3. What is the primary source of energy for ocean waves?

Q4. When the Moon is closest to the Earth, it is said to be in:

Q5. Which of the following factors contributes to the occurrence of tides on Earth?

Frequently asked questions

What are the main movements of ocean water discussed in this chapter?

This chapter discusses three main movements of ocean water: waves, tides, and currents. It explains their formation, causes, and effects on the Earth's climate and navigation.

How are ocean waves formed?

Ocean waves are primarily formed by the energy transferred from the wind to the water surface. The speed, duration, and fetch (distance over which the wind blows) of the wind determine the size and force of the waves.

What causes tides?

Tides are mainly caused by the gravitational pull exerted by the Moon and the Sun on the Earth's oceans. The centrifugal force, resulting from the Earth's rotation, also plays a role in balancing these gravitational forces.

What is the difference between perigee and apogee?

Perigee is the point in the Moon's orbit when it is closest to the Earth, while apogee is the point when it is farthest from the Earth. Similarly, perihelion is when Earth is closest to the Sun, and aphelion is when it's farthest.

How do ocean currents impact coastal climates?

Ocean currents significantly affect coastal temperatures. Warm currents raise temperatures and can lead to warmer, wetter climates, while cold currents lower temperatures and can result in cooler, drier conditions along coastlines.

Are tides important for navigation?

Yes, tides are important for navigation. They can help make rivers navigable for larger vessels, as seen with the Port of Kolkata, which relies on the tidal nature of the Hooghly River.

Important links

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