Movements of Ocean Water Class 11 Important Extra Questions Geography Chapter 14
Movements of Ocean Water Important Extra Questions Very Short Answer Type
Question 1.
What is inner space?
Answer:
The world of oceans and seas is referred to as “inner space,”
Question 2.
What are the important mechanisms by which ocean currents are generated?
Answer:
The important mechanisms are:
The drag of winds over the ocean surface, and
Unequal forces set up by differences in water density.
Question 3.
Classify the ocean currents.
Answer:
The ocean currents may broadly be classified into cold currents and warm currents.
Question 4.
Give the other name of tropical easterlies.
Answer:
Tropical easterlies are also known as trade winds.
Question 5.
Name the force that changes the direction of water drift in oceans.
Answer:
The Coriolis force changes the direction of water drift in oceans.
Question 6.
What kind of currents results due to differences in water density?
Answer:
Differences in water density set currents in a motion described as thermocline currents.
Question 7.
What is ‘gyre’?
Answer:
Due to the Coriolis effect, the moving water turns and follows an elliptical path and it is known as a gyre.
Question 8.
Which current flows as Kuroshio current after reaching the coasts of Taiwan and Japan?
Answer:
The North equatorial current flows as Kuroshio current after reaching the coasts of Taiwan and Japan.
Question 9.
Name the northern and southern branches of North Pacific current.
Answer:
Alaska and California currents respectively.
Question 10.
Define waves.
Answer:
Waves are oscillatory movements in water, where its particles move in a vertical plane, up and down.
Question 11.
What are the progressive waves?
Answer:
Ocean waves produced by winds are called progressive waves.
Question 12.
What is the difference between flood tide and ebb tide?
Answer:
Rise of sea level is called the flood tide and fall is called ebb tide.
Question 13.
Which is the birthplace of common eels?
Answer:
The Sargasso in the western North Atlantic is surrounded by the Florida current. It is often windless and is clocked with seaweed. It is the birthplace of common eels.
Question 14.
Up to what depth in water, the photosynthesis is possible for plants?
Answer:
The sunlight penetrates water up to 900 metres, but only in the top 100 metres is there enough light for plants to do photosynthesis.
Question 15.
When do the tides attain maximum height?
Answer:
Twice a month, when the earth, the moon and the sun are in a straight line.
Question 16.
At what interval of time do the tides occur on each meridian and why?
Answer:
Each meridian has a high and a low tide at an interval of 12 hrs. and 26 minutes, due to rotation of the earth.
Question 17.
Name two types of waves.
Answer:
Transverse waves, and
Longitudinal waves.
Question 18.
What is the main cause of the tide?
Answer:
The gravitational interaction of the earth, the moon and the sun is the main cause of tide.
Question 19.
What are the main processes of cooling of ocean water?
Answer:
Back radiation of heat from the sea surface, convection and evaporation.
Question 20.
What are ocean currents?
Answer:
The ocean currents are the regular movement of the surface of the water in a particular direction.
Question 21.
When does spring tide occur?
Answer:
Springtide occurs in the first and last quarter of the moon and sun are almost in a line.
Question 22.
Where does neap tide occur?
Answer:
When the sun and the moon are at right angles at the earth’s centre, neap tide occurs in the first and the last quarter of the moon.
Question 23.
What is the drift?
Answer:
The motion of the ocean water, generally at low velocity, as a result of surface friction from the prevailing winds.
Question 24.
What is salinity?
Answer:
It is the degree to which water contains dissolved salts.
Movements of Ocean Water Important Extra Questions Short Answer Type
Question 1.
Describe the types of ocean currents and their flow mechanism.
Answer:
Ocean currents are of two types: warm and cold currents. The main currents flow from the low latitudes in tropical zones towards high latitudes in the temperate and sub-polar zones. The cold currents flow from high latitudes to low latitudes.
Question 2.
Give reasons why the height of tidal waves varies from place to place?
Answer:
The height of the tidal waves varies from place to place because of the following reasons:
The relative position of the moon and the sun with respect to the earth,
Distribution of land and ocean on the earth’s surface, and
Irregularities in the configuration of oceans.
Question 3.
What are tides?
Answer:
Tides are periodic rise and fall in the level of water in seas and oceans caused by the differential attraction of the moon and the sun. Twice a day, about every 12 hrs and 26 minutes, the sea level rises and falls. The rise of sea level is called the flood tide and the fall is called the ebb tide.
Question 4.
What is a tidal bore?
Answer:
‘The tidal waves follow the direction of the moon. In certain inland seas, where tidal waves reach from different directions, one can find a number of high tides and low tides. When such waves enter a gulf or river mouths, the tidal crests look like a vertical wall of water rushing upstream, which is known as the tidal bore.
Question 5.
Discuss the impact of prevailing winds on the motion of currents.
Answer:
Air flowing over the water surface exerts a dragging force upon that surface, setting the surface water layer in motion. Prevailing winds, such as the tropical easterlies (trade winds), blowing from east to west, and the middle-latitude westerlies, blowing from west to east, exert a one-way drag on sea surface over a vast expanse of oceans. This drag produces a system of drift currents.
Question 6.
Explain how differences in water density set currents in motion?
Answer:
Differences in water density can also set currents in motion These are described as thermocline currents. A surface water layer in one place may be less dense because it is warmer, or lower in density than the water layer in adjacent place that is colder or has a higher density. The water then moves gently from the region of less to the higher density.
Question 7.
Why the circulation of currents in the Indian ocean is different from the Atlantic and the Pacific oceans?
Answer:
The circulation of currents in the Indian ocean is characteristically different from the Atlantic and Pacific oceans because the Indian ocean is landlocked in the north. The circulation pattern in the northern portion of the Indian ocean changes its direction in response to the seasonal rhythm of the monsoons. There is a clear reversal of currents between winter and summer.
Question 8.
Describe the mechanism of origin of sea waves.
Answer:
It is commonly believed that the waves are generated due to friction on water surface caused by winds. The height of sea waves depends on:
The wind speed,
The duration of wind from a particular direction, and
The fetch or the expanse of water surface over which the wind blows.
Question 9.
Distinguish between progressive and oscillatory waves.
Answer:
The ocean waves produced by winds rapidly through the water are called progressive waves, whereas in oscillatory waves each wave passes a fixed reference point, and the water particles travel through a vertical cycle of motion and return approximately to their original position.
Question 10.
Discuss the properties of waves.
Answer:
Waves are oscillatory movements in water, where its particles move in a vertical plane, up and down. The upper part of the wave is called the crest, and the lower part is called the trough. Each wave has a wavelength, velocity, height and wave period. The distance between two successive crests or two successive troughs is the wavelength. The time taken by a wavelength to pass a fixed point is known as the wave period. The vertical distance between a trough and a crest is called the wave height. The ratio of wavelength to the wave period gives the velocity of the wave.
Question 11.
Distinguish between Swell and Surf.
Answer:
(1) Swells are the wind-generated waves in the
open sea.
(1) Surf also generated by winds but near the beach.(2) They move in a uniform pattern of equivalent period and height.(2) This is foaming water which results from highly dynamic wave capacity.(3) They are generated in the
open ocean
(3) These occur in the breaker zone of a shoreline.
Question 12.
What are the disadvantages of tides?
Answer:
Tides are sometimes harmful to ships and boats.
Tides check the formation of deltas.
Marshes are formed due to accumulation of tidal water.
Tides also hinder fishing.
Question 13.
Why does the temperature of seawater decrease with depth?
Answer:
The temperature of seawater is the same as that of the surface water up to a height of 100 metres. The surface of seawater receives, maximum insolation. As the rays penetrate the water, the heat is reduced by scattering, reflection and diffusion.
Question 14.
How can the velocity of the ocean currents be measured?
Answer:
The ocean currents flow like extensive rivers in the ocean. The rate of flow and the width of the currents, however, are not uniform. The Gulf stream, for example, is 80 km. wide and 1.6 km. deep. The Florida current has a velocity of 10 km. per hour on the surface and 3.5 km. at a depth of 200 m.
Movements of Ocean Water Important Extra Questions Long Answer Type
Question 1.
Write a short note on the vertical circulation of ocean water.
Answer:
Besides the horizontal movement, the vertical circulation of ocean water is also an important phenomenon. Ocean surface is marked with sinking and upwelling caused by wind action, evaporation of surface water, the addition of surface water by rainfall and changes in density due to cooling or warming of the surface layer. A most important cause of the sinking of ocean water on a large scale is cooling of the surface layer by loss of heat to the overlying atmosphere in high latitudes.
During long winters, much heat is lost to space than is gained by solar ^ radiation, thereby the relatively warm surface waters brought polewards v by ocean currents are drilled and increased in density. This water, generally close to the freezing point, sinks to the ocean floor, causing vertical circulation of the water.
Question 2.
Describe the currents of the Pacific ocean in brief.
Answer:
The important currents of the Pacific ocean are North equatorial, Kuroshio current, Alaska current, California current, Oyashio current, Okhotsk current, South equatorial current, South. Pacific current and Peru current.
The North equatorial current from the west coast of Central America reaches the Philippine Island, flowing from east to west in the north Pacific ocean.
Turning northward, the North equatorial current flows along Taiwan and Japan to form Kuroshio current. The currents are influenced by the westerlies from the south-east coast of Japan and tend to flow from west to east as North Pacific current. The current gets bifurcated into the northern and southern branches, called Alaska and California currents respectively after reaching the west coast of N&rth America.
The Alaska current flows anti-clockwise above the coast of British Columbia and Alaska, whereas the California current flows along the coast of California. The cold current, the Oyashio, flows in the North Pacific. Another cold current, named Okhotsk flows in the north Pacific and merges with Oyashio current, which finally sinks beneath the warmer waters of the Kuroshio.

Fig.14.3 current of the Pacific Ocean
The South equatorial current flows in the south Pacific ocean. It flows southward as the East Australian current before meeting the South Pacific current near Tasmania, which flows west to east. Near the south-western coast of South America, it turns north as the Peru Current. It is a cold current that feeds the South equatorial, thus completing the circle.
Question 3.
Distinguish between swash and backwash.
Answer:
When ocean waves arrive at the coast of a continent or island, they encounter shallow Water. The configuration of coast interferes with the progress of the waives. Waves in shallow water are modified into ellipses that become progressively flattered as the coast is approached, As the steeping waves continue to travel shoreward, encountering still shallower water, the crest height increases sharply and the forward slope of the wave becomes greatly steepened. At a critical point, the ‘ waveform disintegrates into a mass of turbulent water called the breaker. Thereafter, it becomes a landward moving sheet of highly turbulent water known as the swash or uprush.
The water then begins to pour seaward down the slope in a reverse flow termed as backwash or back rush. Thus, backwash is the seaward flow of a body of water down the slope after a wave has broken on the beach, in contrast to swash. It may also be called the drag of a recording wave.

Fig. 14.4: Longshore drift showing wave action and the movement of beach materials
Question 4.
Write a short note on a spring tide and neap tide.
Answer:
Tides are the periodic rise and fall in the level of water in seas and oceans caused by the differential attraction of the moon and the sun. Twice a day, about every 12 hrs and 26 minutes, the sea level rises and falls.
Tides do not rise to the same height every day. The relative position of the moon and the sun with respect to the earth is responsible for this variation in the height of tides. On the full moon and the new moon, the moon and the sun are almost in line with the earth, and hence, they exert their combined puli. Therefore, on these two days, tides are the highest and are known as spring tides.
On half-moon, the sun and the moon make a right angle at the earth’s centre. The pulls of the moon and the sun partly cancel each other out. as a result of which there are usually low tides called neap tides. This happens on the first and the last quarter of the lunar month when due to their right angular position to the attraction1 and centrifugal forces of the sun and the moon do not combine. This reduces the height of the tides to the minimum.

Question 5.
If there were no ocean currents, what would have happened to the world? Discuss.
Answer:
The oceans contain about 3% of the total water on earth. This water is always available for evaporation into the atmosphere and its subsequent precipitation on the land and the seas.
The general movement of a mass of ocean water in a fairly defined direction over great distances is called the ocean current. Current ranges in scale from ocean-wide flow system to local currents of small extent and can be generated by several mechanisms.’ Ocean currents are broad of two types: warm and cold currents. The warm currents flow from the low latitudes in tropical zones towards the high latitudes in the temperate and polar zones. The cold currents flow from high latitudes to low latitudes.
Water has an exceptionally great capacity for absorbing heat. The circulation of ocean water through currents helps in distribution of heat received in low latitudes to certain areas of high latitudes. In this way, the oceans modify the climate of the earth. Without ocean currents, this modification of climate would not have been possible.
The distribution of rich fishing grounds in the oceans and seas depends upon the circulation of water of the oceans as they bring nutrients to the surface in some areas. This process of bringing nutrients – both mineral and organic to the surface through the upwelling of water and its circulation is known as the ploughing action of the seas. Ocean currents aid in these processes. The absence of ocean currents would have hampered this process.
Ocean surface is marked with sinking (surges) and upwelling (swells) caused by wind action, evaporation of surface water, the addition of surface water by rainfall and changes in density due to cooling or warming of the surface layer. A most important cause of the sinking of ocean water on a large scale is cooling of the surface layer by loss of heat to the overlying atmosphere in high altitudes.
During long winters, much heat is lost to space, than is gained by solar radiation, thereby relatively warm surface waters brought poleward by ocean currents are chilled and increased in density. This water may be close to the freezing point and, therefore, sinks to the ocean floor. Without ocean currents, all the above activities of the ocean water would not have taken place.
