Movements of ocean water For Class 11 Important Questions

Ans. (a) Undertow

Ans. (c) Semi-diurnal tide

Ans.  (b) salinity and density of water

Ans. (a) Wind

Ans. (b) Gulf stream

Ans. (c) ebb

Ans. (c) Half of the wave height

Ans. (c) Icebergs

Ans. (c) both of these

Ans. (b) 71%

Ans.  (d) Salinity

Ans. (a) The west wind drift

Ans.  (b) flood

Ans. (a) Knots

Ans.  (b) 11033 m.

Ans. (b) 3000-6000 m.

Ans. The important mechanisms are:

1. The drag of winds over the ocean surface, and
2. Unequal forces set up by differences in water density.

Ans.

1. Transverse waves, and
2. Longitudinal waves.

Q 19 –ive reasons why the height of tidal waves varies from place to place?

Ans. The height of the tidal waves varies from place to place because of the following reasons:

1. The relative position of the moon and the sun with respect to the earth,
2. Distribution of land and ocean on the earth’s surface, and
3. Irregularities in the configuration of oceans.

Ans. 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.

Ans. ‘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.

Ans. 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.

Ans. 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.

Ans. 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:

1. The wind speed,
2. The duration of wind from a particular direction, and
3. The fetch or the expanse of water surface over which the wind blows.

Ans. 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.

Ans. 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.

Ans.

Ans.

1. Tides are sometimes harmful to ships and boats.
2. Tides check the formation of deltas.
3. Marshes are formed due to accumulation of tidal water.
4. Tides also hinder fishing.

Ans. 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.

Ans. 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.

Ans. 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.

Ans. 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.

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. Distinguish between swash and backwash.

Ans. 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 increasessharply 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.

Ans. 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.

Ans. 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.