CHAPTER 14 : Movements of Ocean Water NCERT SOLUTION CLASS 11TH GEOGRAPHY| EDUGROWN NOTES

SHORT ANSWER TYPE QUESTION:

Q1. What are waves?
Answer
Waves are energy, not the water which moves across the ocean surface. It generated by wind driving against water.

Q2. Where do waves in the ocean get their energy from?

Answer

Wind provides energy to the waves. Wind causes waves to travel in the ocean and the energy is released on shorelines.

Q3. What are tides?

Answer

The periodical rise and fall of the sea level, once or twice a day, mainly due to the attraction of the sun and the moon, is called a tide.

Q4. How are tides caused?

Answer

The tides are caused by the gravitational pull of the sun and the moon and the centrifugal force

Q5.How are tides related to navigation?

Answer

Tides helps the navigators and fishermen plan their activities. Tidal flows are of great importance in navigation. Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour.

Q6. How do currents affect the temperature? How does it affect the temperature of coastal areas in the N. W. Europe?

Answer

The currents directly affect the temperature. The temperature varies depending on whether currents are warm or cold:
• Cold currents bring cold water into warm water areas. These currents are usually found on the west coast of the continents in the low and middle latitudes (true in both hemispheres) and on the east coast in the higher latitudes in the Northern Hemisphere
• Warm currents bring warm water into cold water areas and are usually observed on the east coast of continents in the low and middle latitudes (true in both hemispheres). In the northern hemisphere they are found on the west coasts of continents in high latitudes.

In North West Europe, warm currents are present which increase the temperature in coastal areas in the North West Europe.

Q7.What are the causes of currents?
Answer

Oceans currents are caused by two forces mainly:
(i) primary forces that initiate the movement of water
(ii) secondary forces that influence the currents to flow.

The primary forces that influence the currents are:

• Heating by solar energy:  Heating by solar energy causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.

• Wind: It blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course

• Gravity: It tends to pull the water down the pile and create gradient variation.

• Coriolis force: This intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called Gyres. These produce large circular currents in all the ocean basins.

The secondary forces that influence the currents are:

• Difference in water density: It affect vertical mobility of ocean currents. Denser water tends to sink, while relatively lighter water tends to rise.

• Difference in Salinity: Water with high salinity is denser than water with low salinity and in the same way cold water is denser than warm water.

Long Answer Type Questions :

Q1.In how many categories can tides be classified on the basis of their height and frequency?
Answer:

• Semi-diurnal tide: It is the most common tidal pattern, featuring two high tides and two low tides each day. The successive high or low tides are approximately of the same height.
• Diurnal tide: There is only one high tide and one low tide during each day. The successive high and low tides are approximately of the same height.
• Mixed tide: Tides having variations in height are known as mixed tides. These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.
• Spring tides: The position of both the sun and the moon in relation to the earth has direct bearing on tide height. When the sun, the moon and the earth are in a straight line, the height of the tide will be higher. These are called spring tides.
• Neap tides: Wlien the sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another. The moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull. These are called neap tides.

Q2.White the characteristics of waves in the oceanic water.
Answer:
Characteristics of waves in the oceanic water are given below:

• The highest and lowest points of a wave are called the crest and trough.
• Wave height is the vertical distance from the bottom of a trough to the top of a crest of a wave.
• Wave amplitude is one-half of the wave height.
• Wave period is merely the time interval between two successive wave crests.
• Wavelength is the horizontal distance between two successive crests.
• Wave speed is the rate at which the wave moves through the water, and is measured in knots.
• Wave frequency is the number of waves passing a given point during a one- second time interval.

Q3.Explain how do heating of solar energy, wind, gravitation and coriolis force affect the ocean currents.
Answer:
Heating by solar energy: Heating by solar energy causes the water to expand, that is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope.

• Wind: Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.
• Gravity: Gravity tends to pull the water down the pile and create gradient variation.
• The Coriolis force: The coriolis intervenes and cause the water to move to the right in the northern hemisphere and to the left in the southern hemisphere.

Q4.Differentiate between warm currents and cold currents.
Answer:

S.no.	Warm currents	Cold currents
1.	They flow from equatorial regions to high latitudes.	They flow from polar region to low latitudes.
2.	Its temperature is higher than the surrounding water.	Its temperature is below than the surrounding water.
3.	It raises the temperature of coastal areas and are observed normally on the east coast of lower and middle latitude.	It reduces the temperature of the coastal area and are observed on the west of continent in lower and middle latitudes.
4.	Winds passing over warm currents absorb a good amount of moisture and bring heavy rainfall on the coastal areas.	Winds passing over cold currents becomes dry and little rainfall on the coaarea.
5.	Warm currents are of great help to navigation because they melt ice bergs.	Cold currents hinder navigation because they create ice bergs.
6.	Warm currents keep the ports open in the polar regions free from ice.	Cold currents make the parts unoperational in lower latitudes as they are ice bound.