Source: NCERT Official Textbook
The second major movement is Tides, the periodic rise and fall of sea level caused primarily by the gravitational attraction of the moon and, to a lesser extent, the sun, combined with centrifugal force. This creates two tidal bulges on Earth.
The chapter classifies tides by frequency (semi-diurnal, diurnal, mixed) and by the sun-moon-earth alignment (Spring Tides during new/full moon and Neap Tides when the sun and moon are at right angles). It highlights the importance of tides for navigation, fishing, desilting estuaries, and generating tidal power.
Finally, the chapter covers Ocean Currents, the steady, river-like flows of water. Their movement is initiated by primary forces: solar heating, wind, gravity, and the Coriolis force (which creates large circular Gyres).
Currents are classified by depth (surface vs. deep water) and temperature (warm vs. cold). The distribution of major currents corresponds to global wind patterns.
The chapter concludes by explaining the significant effects of currents on coastal climates—cooling west coasts in the tropics and warming east coasts in higher latitudes—and their role in creating fertile fishing grounds where warm and cold currents mix.
Which movement of ocean water refers to the continuous flow of a huge amount of water in a definite direction? (Pg. 1)
What is the primary source of energy for waves? (Pg. 1)
The horizontal distance between two successive wave crests is called: (Pg. 2)
The ‘tide-generating’ force is the difference between: (Pg. 2)
Which bay is famous for having the highest tides in the world? (Pg. 3)
Spring tides occur: (Pg. 3)
What are the primary forces that initiate the movement of ocean currents? (Pg. 4)
Which type of current brings cold water into warm water areas and is usually found on the west coast of continents in low/middle latitudes? (Pg. 4)
The mixing zones of warm and cold currents are favourable for the growth of planktons because they help to: (Pg. 5)
(Exercise) Upward and downward movement of ocean water is known as the: (Pg. 6)
(Exercise) Spring tides are caused: (Pg. 6)
(Exercise) The distance between earth and moon is minimum when the moon is in: (Pg. 6)
(Exercise) The earth reaches its perihelion in: (Pg. 6)
The vertical motion of ocean water that refers to the rise and fall of sea level is called ______. (Pg. 1) Page 108
When a wave approaches the beach, it slows down due to friction with the ______. (Pg. 1) Page 108
Wave ______ is one-half of the wave height. (Pg. 2) Page 109
The study of tides is complex due to great variations in frequency, magnitude, and ______. (Pg. 2) Page 109
Tides with two high and two low tides each day, with successive highs/lows of similar height, are called ______ tides. (Pg. 3) Page 110
The time between low tide and high tide, when the water level is rising, is called the ______. (Pg. 3) Page 110
Large circular currents in ocean basins caused by the accumulation of water and the Coriolis force are called ______. (Pg. 4) Page 111
The speed of a current is referred to as its ______. (Pg. 4) Page 111
The major ocean currents are greatly influenced by the stresses exerted by the prevailing winds and the ______ force. (Pg. 5) Page 112
(Exercise) Waves in the ocean get their energy from ______. (Pg. 6) Page 113
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