NCERT Solutions for Class 11 Geography Chapter 13: Movements of Ocean Water (NCERT 2026–27)

These Class 11 Geography Chapter 13 solutions cover Movements of Ocean Water from Fundamentals of Physical Geography, the NCERT textbook for the 2026–27 session. The chapter explains the three great movements of sea water — waves, tides and ocean currents — their characteristics, the forces that cause them, the different types of tides and currents, and the effects of ocean currents on climate and fishing. Below you get step-by-step answers to every NCERT exercise question reproduced verbatim, plus key terms, extra practice, MCQs, Assertion–Reason questions and FAQs.

Class: 11 Subject: Geography Book: Fundamentals of Physical Geography Chapter: 13 Title: Movements of Ocean Water Session: 2026–27
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Class 11 Geography Chapter 13 – Overview

Chapter 13, Movements of Ocean Water, shows that ocean water is dynamic, with movements driven by its physical characteristics (temperature, salinity, density) and by external forces (the sun, the moon and the winds). These movements are of two kinds: horizontal motion — the ocean currents and waves — and vertical motion — the tides and the upwelling and sinking of water. Waves are energy (not water) moving across the surface, caused mainly by wind; their crest, trough, height, period, wavelength and speed describe them. Tides are the periodical rise and fall of sea level caused by the gravitational pull of the moon and the sun together with the centrifugal force, producing two tidal bulges; they are classified by frequency (semi-diurnal, diurnal, mixed) and by the sun–moon–earth position (spring and neap tides). Ocean currents are the regular flow of water in a definite direction, driven by primary forces (solar heating, wind, gravity, the Coriolis force) and secondary forces (density and gravity differences); they are classed as surface/deep and as warm/cold, and they strongly influence coastal climate, fog and the world’s best fishing grounds.

Key Terms & Concepts

Waves: the horizontal motion of water in which energy — not the water itself — moves across the ocean surface; water particles travel only in small circles as a wave passes.

Crest and trough: the highest and lowest points of a wave respectively. Wave height is the vertical distance from the bottom of a trough to the top of a crest; wave amplitude is one-half of the wave height.

Wave period: the time interval between two successive crests (or troughs) passing a fixed point. Wavelength is the horizontal distance between two successive crests. Wave speed (measured in knots) is the rate at which a wave moves through the water; wave frequency is the number of waves passing a point in one second.

Tides: the periodical rise and fall of the sea level, once or twice a day, mainly due to the gravitational attraction of the moon and (to a lesser extent) the sun, together with centrifugal force.

Surges: movements of water caused by meteorological effects (winds and atmospheric-pressure changes); unlike tides, surges are not regular.

Tidal bulge & tide-generating force: the gravitational pull and the centrifugal force together create two tidal bulges — one facing the moon, one on the opposite side. The ‘tide-generating’ force is the difference between the moon’s gravitational attraction and the centrifugal force.

Types by frequency: semi-diurnal (two high and two low tides daily, of nearly equal height), diurnal (one high and one low tide each day), and mixed (tides of varying height).

Spring and neap tides: spring tides occur when the sun, moon and earth are in a straight line (full moon and new moon), giving the highest tides; neap tides occur when the sun and moon are at right angles, giving lower tides, about seven days after spring tides.

Perigee/apogee and perihelion/aphelion: tidal ranges are greatest when the moon is nearest the earth (perigee) and when the earth is nearest the sun (perihelion, around 3 January), and least at apogee and aphelion (around 4 July).

Ebb and flow (flood): the falling water between high and low tide is the ebb; the rising water between low and high tide is the flow or flood.

Ocean currents: the regular, definite flow of a volume of water along a path and direction. Driven by primary forces (solar heating, wind, gravity, the Coriolis force) and secondary forces (density and gravity differences). Large circular currents are called gyres; current speed is called its drift.

Warm and cold currents: warm currents carry warm water into cold areas (mostly along east coasts of continents in low/middle latitudes); cold currents carry cold water into warm areas (mostly along west coasts in low/middle latitudes).

NCERT Exercises — Full Solutions

All questions below are reproduced verbatim from the NCERT textbook’s end-of-chapter Exercises. Answers are original, written in exam-ready style.

1. Multiple choice questions

(i) Upward and downward movement of ocean water is known as the: (a) tide (b) current (c) wave (d) none of the above

ANSWER (a) tide. Tides are the vertical motion of ocean water — the rise and fall (upward and downward movement) of the sea level — whereas currents and waves are horizontal motions of water.

(ii) Spring tides are caused: (a) As result of the moon and the sun pulling the earth gravitationally in the same direction. (b) As result of the moon and the sun pulling the earth gravitationally in the opposite direction. (c) Indention in the coast line. (d) None of the above.

ANSWER (a) As a result of the moon and the sun pulling the earth gravitationally in the same direction. When the sun, moon and earth lie in a straight line (at full moon and new moon), their gravitational pulls combine, raising the tide higher — these are spring tides.

(iii) The distance between the earth and the moon is minimum when the moon is in: (a) Aphelion (b) Perigee (c) Perihelion (d) Apogee

ANSWER (b) Perigee. Perigee is the point in the moon’s orbit closest to the earth; at this time unusually high and low tides occur because the tidal range is greater than normal. (Apogee is the farthest point; perihelion and aphelion refer to the earth’s distance from the sun.)

(iv) The earth reaches its perihelion in: (a) October (b) September (c) July (d) January

ANSWER (d) January. The earth is closest to the sun (perihelion) around 3rd January each year, when tidal ranges are much greater. It is farthest from the sun (aphelion) around 4th July.

2. Answer the following questions in about 30 words.

(i) What are waves?

ANSWER Waves are the horizontal movement of energy — not the water itself — across the ocean surface. Water particles move only in small circles as a wave passes, while the wave train travels forward.

(ii) Where do waves in the ocean get their energy from?

ANSWER Most ocean waves get their energy from the wind blowing over the water surface. Friction between wind and water transfers energy; waves keep growing larger as long as they absorb energy from the wind.

(iii) What are tides?

ANSWER Tides are the periodical rise and fall of the sea level, once or twice a day, caused mainly by the gravitational attraction of the moon and the sun together with the centrifugal force acting on the earth.

(iv) How are tides caused?

ANSWER Tides are caused by the gravitational pull of the moon (chiefly) and the sun, together with the centrifugal force. These create two tidal bulges — one facing the moon and one on the opposite side — producing the rise and fall of the sea.

(v) How are tides related to navigation?

ANSWER Because tides can be predicted accurately in advance, navigators and fishermen plan their activities by them. High tides help ships cross shallow ‘bars’ at the entrance of harbours and estuaries, and tides keep channels desilted.

3. Answer the following questions in about 150 words.

(i) How do currents affect the temperature? How does it affect the temperature of coastal areas in the N. W. Europe?

ANSWER Ocean currents act like a giant conveyor belt that transports heat from one latitude belt to another, in a way similar to the general circulation of the atmosphere. Warm currents carry warm water from the equatorial and tropical regions towards the poles, raising the temperature of the coasts they pass; cold currents carry cold water from polar regions towards the equator, lowering the temperature of the coasts they bathe. Thus warm currents give east coasts of continents in tropical latitudes warm, rainy climates, while cold currents make west coasts cool, foggy and often arid. In north-west Europe, the warm North Atlantic Drift (an extension of the Gulf Stream) flows along the coast, carrying warm water from the lower latitudes polewards. This keeps the coasts of Britain, Norway and the rest of north-west Europe much warmer than their high latitude would suggest. As a result, ports there remain ice-free in winter, winters are mild, and the region enjoys a marine climate with a narrow annual range of temperature.

(ii) What are the causes of currents?

ANSWER Ocean currents are caused by two sets of forces — primary forces that initiate the movement of water and secondary forces that influence how the currents flow. Primary forces: (i) Heating by solar energy — water expands on heating, so near the equator the ocean stands about 8 cm higher than in the middle latitudes, creating a slight slope down which water flows. (ii) Wind — wind blowing over the surface pushes the water along, and friction sets the water in motion. (iii) Gravity — gravity pulls the piled-up water down, creating gradient variations. (iv) Coriolis force — this deflects the moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, forming large circular currents called gyres. Secondary forces: differences in water density and gravity. Water of high salinity or low temperature is denser and tends to sink, while warmer, less-saline water rises. Cold dense water sinking at the poles and warm water rising near the equator set up the deep-water circulation of the oceans.

Project Work

(i) Visit a lake or a pond and observe the movement of waves. Throw a stone and notice how waves are generated.

HOW TO DO IT This is a field activity, so record what you actually observe. When you throw a stone into still water, it disturbs the surface and energy spreads outward as a series of concentric circular ripples (waves) from the point of impact. Notice that the ripples (the energy) travel outward, but a floating leaf only bobs up and down in small circles — it does not move outward with the wave. This shows the key idea of the chapter: waves carry energy, not the water itself. Note how the ripples grow wider and weaker as they move away, and how a breeze creates many small ripples across the surface.

(ii) Take a globe and a map showing the currents of the oceans. Discuss why certain currents are warm or cold and why they deflect in certain places and examine the reasons.

HOW TO DO IT Using the globe and a current map (Figure 13.3 in the textbook), trace the major currents. A model discussion: currents flowing away from the equator (e.g. the Gulf Stream, Kuroshio, Brazil current) are warm because they carry water heated in the tropics; currents flowing towards the equator (e.g. the Labrador, California, Benguela, Humboldt currents) are cold because they bring polar water. Mark how warm currents hug the east coasts and cold currents the west coasts of continents in low and middle latitudes. For deflection, point out that currents do not flow straight: the Coriolis force turns them to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, so they curve into large circular gyres. The shapes of the continents and the prevailing winds also deflect them. This explains why the warm current of the North Atlantic swings towards Europe while a cold current returns along the American coast.

Extra Practice Questions

Short Answer Type Questions

Q1. Distinguish between waves and currents.

ANSWERIn ocean currents, a huge volume of water actually moves ahead from one place to another in a definite direction. In waves, the water does not move forward — only the energy (the wave train) moves ahead, while water particles travel in small circles. Both are horizontal motions of ocean water.

Q2. What are surges, and how do they differ from tides?

ANSWERSurges are movements of water caused by meteorological effects such as winds and changes in atmospheric pressure. Unlike tides, surges are not regular and cannot be predicted by the earth–moon–sun positions, whereas tides are the regular, predictable rise and fall of the sea level.

Q3. Name and define the three types of tides based on frequency.

ANSWER(i) Semi-diurnal tide — two high and two low tides each day, of nearly equal height (the most common). (ii) Diurnal tide — only one high and one low tide each day. (iii) Mixed tide — tides showing variations in height, common along the west coast of North America and Pacific islands.

Q4. Differentiate between spring tides and neap tides.

ANSWERSpring tides occur when the sun, moon and earth are in a straight line (full moon and new moon); the combined pull gives the highest tides. Neap tides occur when the sun and moon are at right angles to the earth; their forces partly cancel out, giving lower-than-average tides about seven days after spring tides.

Q5. State two ways in which tides are useful to people.

ANSWER(i) Tides help navigation — high tides allow ships and boats to cross shallow bars and enter harbours and estuaries, and they desilt sediments from river mouths. (ii) Tides are used to generate tidal electrical power (as in Canada, France, Russia and China, and the Durgaduani project in the Sunderbans).

Long Answer Type Questions

Q1. Describe the chief characteristics of a wave.

ANSWERA wave is described by several measurable features. The crest and trough are the highest and lowest points of a wave. Wave height is the vertical distance from the bottom of a trough to the top of a crest, and wave amplitude is one-half of the wave height. Wave period is the time interval between two successive crests (or troughs) passing a fixed point, while wavelength is the horizontal distance between two successive crests. Wave speed, measured in knots, is the rate at which the wave moves through the water, and wave frequency is the number of waves passing a given point in one second. The maximum height of a wave is determined by the strength of the wind, how long it blows and the area over which it blows. Importantly, in a wave it is the energy that moves forward, not the water; water particles only move in small circles, and as a wave nears the shore it slows due to friction with the sea floor and finally breaks.

Q2. Explain how the gravitational pull and the centrifugal force together create tides.

ANSWERTides arise mainly from the moon’s gravitational pull (the sun’s pull is smaller) acting along with the centrifugal force that counterbalances gravity in the earth–moon system. Together these create two tidal bulges. On the side of the earth facing the moon, the moon’s attractive force is greater than the centrifugal force, so there is a net force producing a bulge towards the moon. On the opposite side, the moon’s attraction is weaker (being farther away), so the centrifugal force dominates and produces a second bulge away from the moon. The ‘tide-generating’ force is the difference between the moon’s gravitational attraction and the centrifugal force. The horizontal tide-generating forces are more important than the vertical ones in raising the bulges. The shape of bays and estuaries can magnify tides — funnel-shaped bays greatly increase tidal magnitudes, as at the Bay of Fundy, where tidal bulges reach 15–16 m.

Q3. Discuss the effects of ocean currents on human life and climate.

ANSWEROcean currents have many direct and indirect effects. On climate: warm currents flowing along east coasts of continents in tropical and subtropical latitudes give warm, rainy climates; in higher latitudes warm waters (such as those reaching north-west Europe) cause a mild marine climate with cool summers and mild winters and a narrow annual temperature range. Cold currents bordering west coasts in tropical latitudes give relatively low temperatures, frequent fog and generally arid conditions, since the cool water reduces evaporation. On fishing: the mixing of warm and cold currents replenishes oxygen and favours the growth of plankton, the primary food of fish; the world’s best fishing grounds (such as off Newfoundland and Japan) lie in these mixing zones. On navigation and trade: currents speed or hinder shipping, and they distribute heat around the globe much as the atmosphere does, moderating climates worldwide.

MCQs & Assertion–Reason

1. In a wave, what actually moves across the ocean surface?

(a) the water itself    (b) energy    (c) salt    (d) the sea floor

2. One-half of the wave height is called the:

(a) wavelength    (b) wave period    (c) wave amplitude    (d) wave frequency

3. Horizontal motion of ocean water includes:

(a) tides only    (b) waves and currents    (c) upwelling    (d) sinking of surface water

4. The most common tidal pattern, with two high and two low tides each day, is the:

(a) diurnal tide    (b) mixed tide    (c) semi-diurnal tide    (d) spring tide

5. Neap tides occur when the sun and the moon are:

(a) in a straight line    (b) at right angles to each other    (c) at perigee    (d) at perihelion

6. The world’s highest tides (15–16 m) occur in the:

(a) Bay of Bengal    (b) Bay of Fundy    (c) Gulf of Mexico    (d) Persian Gulf

7. Which of the following is a primary force that initiates ocean currents?

(a) density difference    (b) salinity difference    (c) the Coriolis force    (d) all of the above

8. Large circular accumulations of water and the flow around them are called:

(a) surges    (b) gyres    (c) drifts    (d) bulges

9. Surface currents make up about what percentage of all the water in the ocean?

(a) 10 per cent    (b) 40 per cent    (c) 70 per cent    (d) 90 per cent

10. The falling water level between high tide and low tide is called the:

(a) flood    (b) flow    (c) ebb    (d) surge

Answer key: 1-(b), 2-(c), 3-(b), 4-(c), 5-(b), 6-(b), 7-(c), 8-(b), 9-(a), 10-(c).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: In a wave the water does not move forward with the wave.

Reason: A wave is the movement of energy across the surface, while water particles only travel in small circles.

A-R 2. Assertion: Spring tides are higher than neap tides.

Reason: At spring tides the sun, moon and earth are in a straight line and their gravitational pulls combine.

A-R 3. Assertion: Tides can be predicted accurately well in advance.

Reason: Tides are caused by the earth–moon–sun positions, which are known accurately.

A-R 4. Assertion: Warm currents are usually found along the west coasts of continents in low and middle latitudes.

Reason: The Coriolis force deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

A-R 5. Assertion: The best fishing grounds of the world lie where warm and cold currents meet.

Reason: The mixing of warm and cold currents replenishes oxygen and favours the growth of plankton.

Answer key: 1-(A), 2-(A), 3-(A), 4-(D), 5-(A).

Exam Tips & Common Mistakes

How to score full marks in this chapter

Keep the big classification clear: ocean water moves by horizontal motion (waves and currents) and vertical motion (tides). Memorise the seven wave characteristics (crest, trough, height, amplitude, period, wavelength, speed, frequency) and the two tide classifications (by frequency: semi-diurnal, diurnal, mixed; by sun–moon position: spring, neap). For tide diagrams, always mention the two bulges and the balance of gravitational and centrifugal forces. For currents, learn the four primary forces and link warm/cold currents to coastal climate (north-west Europe = North Atlantic Drift). Use textbook examples — Bay of Fundy, Durgaduani tidal power, perigee/perihelion — to show depth.

Common mistakes to avoid

  • Saying the water moves forward in a wave — it is the energy that moves; water particles move in small circles.
  • Confusing spring tides (straight line, highest) with neap tides (right angles, lowest).
  • Mixing up perigee/apogee (moon–earth distance) with perihelion/aphelion (earth–sun distance).
  • Forgetting that warm currents mostly border east coasts and cold currents west coasts in low/middle latitudes.
  • Writing only gravitational force for tides — always include the centrifugal force and the two bulges.
  • Confusing ebb (falling water) with flow/flood (rising water).

Frequently Asked Questions

What is Chapter 13 of Class 11 Geography about?

Chapter 13, Movements of Ocean Water, deals with the three movements of sea water — waves, tides and ocean currents. It explains their characteristics, the forces (wind, gravity, the moon and sun, and the Coriolis force) that cause them, the types of tides and currents, and the effects of currents on climate and fishing.

What is the difference between spring tides and neap tides?

Spring tides occur when the sun, moon and earth are in a straight line (at full moon and new moon), so their gravitational pulls combine to give the highest tides. Neap tides occur when the sun and moon are at right angles, so their forces partly cancel, giving lower tides about seven days after the spring tides.

How do ocean currents affect the climate of north-west Europe?

The warm North Atlantic Drift (an extension of the Gulf Stream) flows along north-west Europe, carrying warm water from lower latitudes polewards. This keeps the coasts of Britain and Norway much warmer than their latitude would suggest, gives mild winters, a marine climate and ice-free ports in winter.

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