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Movements of Ocean Water – Class 11 Geography notes, important questions and MCQs

NCERT Class 11 Geography, chapter 13. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Ocean water is always in motion through waves, tides and currents. Waves are mainly caused by wind, tides by the gravitational pull of the Moon and the Sun, and currents by wind, differences in temperature and salinity, and the Earth's rotation. Ocean currents carry heat and strongly influence the climate of coastal regions.

Waves and tides

Waves are formed as wind transfers energy to the water surface; the water particles move in circles while the energy moves forward.
Tides are the periodic rise and fall of sea level, caused mainly by the Moon's gravitational pull and partly by the Sun.
Spring tides occur at new moon and full moon, when the Sun, Moon and Earth are in a line, and are higher; neap tides occur at the first and third quarters, when the Sun and Moon are at right angles, and are lower. The Bay of Fundy in Canada has the highest tides.

Ocean currents

Currents are like rivers in the ocean, driven by primary forces such as solar heating, wind, gravity and the Coriolis force, and influenced by differences in density.
Warm currents flow from low to high latitudes (e.g. Gulf Stream, Kuroshio); cold currents flow from high to low latitudes (e.g. Labrador, Peru or Humboldt, Benguela, Canary).
Warm currents raise coastal temperatures and bring rain; cold currents lower temperatures and help form coastal deserts; the meeting of warm and cold currents creates good fishing grounds, such as off Newfoundland.

Key terms

Tide: periodic rise and fall of sea level due to the Moon's and Sun's attraction
Spring tide: a very high tide when the Sun, Moon and Earth are in a line
Neap tide: a lower tide when the Sun and Moon are at right angles to the Earth
Ocean current: a continuous flow of ocean water in a definite direction
Gulf Stream: a warm current in the North Atlantic Ocean

Important questions with answers

What is the difference between spring tides and neap tides?2 marks

Spring tides are very high high tides and very low low tides that occur at new moon and full moon, when the Sun, Moon and Earth are in a straight line. Neap tides have a smaller range and occur when the Sun and Moon are at right angles to the Earth, during the first and third quarters.

What are the effects of ocean currents?3 marks

Warm currents raise the temperature of coastal areas and bring rain, keeping some ports ice-free; cold currents lower temperatures and contribute to coastal deserts. Mixing of warm and cold currents creates rich fishing grounds, while currents also affect navigation and the distribution of marine life.

Explain the causes and types of ocean currents.5 marks

Ocean currents are large masses of water moving continuously in a definite direction. They are influenced by primary forces and secondary forces. Primary forces include heating by solar energy, which causes water to expand near the equator and creates a slight slope; wind, which pushes surface water in the direction it blows, as the trade winds and westerlies do; gravity, which pulls water down the slope; and the Coriolis force, which deflects currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, creating large circular gyres. Secondary forces include differences in water density due to temperature and salinity, which cause dense, cold, salty water to sink and less dense water to rise. Currents are classified by depth into surface currents and deep-water currents, and by temperature into warm and cold currents. Warm currents, such as the Gulf Stream, North Atlantic Drift, Kuroshio and Brazil Current, flow from low latitudes towards higher latitudes along the eastern coasts of continents in low and middle latitudes. Cold currents, such as the Labrador, Canary, Benguela, Peru and California currents, flow from higher to lower latitudes, mostly along the western coasts of continents. These currents redistribute heat and influence climate, fishing and navigation.

Quick revision

Waves: wind energy; particles move in circles.
Tides: Moon and Sun; spring and neap tides.
Currents: warm and cold; forces.
Effects on climate and fishing.

Exam tips

Make a table of major warm and cold currents with oceans.
Remember: spring tides at new and full moon.

Practice MCQs

Waves are mainly caused by
1. earthquakes only
2. wind
3. the Moon
4. salinity
Show answer
Answer: (b) wind. Wind transfers energy to water.
Tides are caused mainly by the gravitational pull of the
1. Sun
2. Moon
3. Mars
4. Jupiter
Show answer
Answer: (b) Moon. The Sun also contributes.
The Gulf Stream is a
1. cold current
2. warm current
3. tide
4. wave
Show answer
Answer: (b) warm current. It flows in the North Atlantic.
Spring tides occur at
1. new moon and full moon
2. first quarter only
3. third quarter only
4. every noon
Show answer
Answer: (a) new moon and full moon. The Sun, Moon and Earth are in a line.
Which is a cold current
1. Kuroshio
2. Gulf Stream
3. Brazil Current
4. Labrador Current
Show answer
Answer: (d) Labrador Current. It flows from the Arctic.
The place with the highest tides in the world is the
1. Gulf of Khambhat
2. Mediterranean Sea
3. Red Sea
4. Bay of Fundy
Show answer
Answer: (d) Bay of Fundy. It is in Canada.
Why are rich fishing grounds found off Newfoundland
1. only cold water
2. deep trenches
3. absence of plankton
4. mixing of the warm Gulf Stream and the cold Labrador Current
Show answer
Answer: (d) mixing of the warm Gulf Stream and the cold Labrador Current. Mixing supports plankton growth.
Coastal deserts such as the Atacama are linked to
1. warm currents
2. cold currents along the coast
3. high tides
4. tsunamis
Show answer
Answer: (b) cold currents along the coast. Cold currents cool and dry the air.

All chapters of Class 11 Geography

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.