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Spring tides are caused :
  •  As result of the moon and the sun pulling the earth gravitationally in the same direction.
  • As result of the moon and the sun pulling the earth gravitationally in the opposite direction.
  •  Indention in the coast line.
  • None of the above.

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Upward and downward movement of ocean water is known as the :
  • Tide 
  • Current
  • Wave 
  • None of the above

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 The distance between the earth and the moon is minimum when the moon is in :
  • Aphelion 
  • Perihelion
  • Perigee 
  • Apogee

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What are the causes of currents ?

Following are the causes of currents:


i. Prevailing winds: Prevailing winds influence the ocean currents more than any other single factor. These winds blow in a particular direction and drag the surface water due to the force of friction. This leads to the formation of ocean currents.

ii.Temperature difference: Warm water is lighter and rises but the cold water is denser and sinks. This makes the difference in the levels of a sea. Warm equatorial water moves polewards along the surface while the cold water from the poles move along the bottom towards the equator.

iii. Difference in salinity: Waters of high salinity are denser and heavier while the waters of low salinity are lighter. As a result light water with less salinity rushes towards the high salinity water and a current is formed.

iv. Coriolis effect: Due to the Coriolis effect the moving water turns and flows elliptical path known as gyre. Water circulates in these gyres in clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.


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


Currents affect the temperature directly. The warm currents raise and the cold currents lower the temperature of the neighbouring islands. The winds blowing over the cold current carry low temperature and have a cooling effect. Wind blowing over warm currents have a warming effect and raise the winter temperature of regions situated in higher latitudes.


The North-West Europe's coast remains open due to the Gulf Stream (warm current) and has an ideal climate due to the moderating effect of North Atlantic Drift.
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