Movements of Ocean WaterClass 11 Fundamentals of Physical Geography NCERT Solutions
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Solution 1 of 13
Q11. Multiple choice questions.
(i) Upward and downward movement of ocean water is known as the :
(a)
tide
(b)
current
(c)
wave
(d)
none of the above
Solution
(a) tide
The source content states that vertical motion refers to the rise and fall of water in the oceans and seas, and this periodical rise and fall is called a tide. Currents and waves are described as forms of horizontal motion.
Q21. Multiple choice questions.
(ii) Spring tides are caused :
(a)
As result of the moon and the sun pulling the earth gravitationally in the same direction.
(b)
As result of the moon and the sun pulling the earth gravitationally in the opposite direction.
(c)
Indention in the coast line.
(d)
None of the above.
Solution
(a) As result of the moon and the sun pulling the earth gravitationally in the same direction.
According to the text, spring tides occur when the sun, the moon, and the earth are in a straight line. In this alignment, their combined gravitational forces pull in the same line of action, resulting in higher tides.
Q31. Multiple choice questions.
(iii) The distance between the earth and the moon is minimum when the moon is in :
(a)
Aphelion
(b)
Perigee
(c)
Perihelion
(d)
Apogee
Solution
(b) Perigee
The text explicitly states, "Once in a month, when the moon's orbit is closest to the earth (perigee), unusually high and low tides occur." Apogee is when the moon is farthest from the earth. Perihelion and aphelion refer to the earth's distance from the sun.
Q41. Multiple choice questions.
(iv) The earth reaches its perihelion in:
(a)
October
(b)
September
(c)
July
(d)
January
Solution
(d) January
The chapter mentions, "When the earth is closest to the sun (perihelion), around 3rd January each year, tidal ranges are also much greater..."
Q12. Answer the following questions in about 30 words.
(i) What are waves?
Solution
Waves are the horizontal motion of energy across the ocean surface, not the water itself. Water particles move in a small circle as a wave passes, but it is the wave energy that travels forward. Most waves are generated by the force of wind acting on the water surface.
Q22. Answer the following questions in about 30 words.
(ii) Where do waves in the ocean get their energy from?
Solution
Waves in the ocean primarily get their energy from the wind. Wind blowing against the surface of the water transfers its energy to the water, causing ripples that grow into larger waves. The strength and duration of the wind determine the size and energy of the waves.
Q32. Answer the following questions in about 30 words.
(iii) What are tides?
Solution
Tides are the periodical rise and fall of the sea level, which typically occurs once or twice a day. They are primarily caused by the gravitational attraction of the moon and, to a lesser extent, the sun on the Earth's oceans.
Q42. Answer the following questions in about 30 words.
(iv) How are tides caused?
Solution
Tides are caused by the combined effects of the gravitational forces exerted by the moon and the sun, and the centrifugal force due to the Earth's rotation. These forces together create tidal bulges on opposite sides of the Earth, leading to the regular rise and fall of sea level.
Q52. Answer the following questions in about 30 words.
(v) How are tides related to navigation?
Solution
Tides are crucial for navigation as their predictable nature helps navigators and fishermen plan their activities. High tides are important for ships entering or leaving harbours with shallow bars at the entrance. Tidal currents can also assist or hinder the movement of vessels in bays and estuaries.
Q13. Answer the following questions in about 150 words.
(i) How do currents affect the temperature? How does it affect the temperature of coastal areas in the N. W. Europe?
Solution
Ocean currents significantly affect temperature by transporting vast amounts of water, and therefore heat, from one part of the globe to another. This process is similar to the general circulation of the atmosphere.
- Warm currents, like those originating in equatorial regions, move towards the poles, bringing warmer water into colder regions. This raises the temperature of the coastal areas they flow past.
- Cold currents, originating in polar regions, move towards the equator, bringing cold water into warmer areas and lowering the temperatures of adjacent coastlines.
Coastal areas of Northwestern Europe are a prime example of this effect. This region is bordered by the North Atlantic Drift, a warm current that is an extension of the Gulf Stream. This warm water current brings a moderating influence to the climate of N.W. Europe. It causes the region to have a distinct marine climate characterized by relatively mild winters and cool summers, with a narrow annual temperature range. Without this warm current, winters in countries like the UK and Norway would be significantly colder.
Q23. Answer the following questions in about 150 words.
(ii) What are the causes of currents?
Solution
Ocean currents are influenced by two types of forces: primary forces that initiate the movement of water and secondary forces that influence its flow. The primary forces that cause ocean currents are:
- Heating by Solar Energy: Solar energy heats the water near the equator, causing it to expand. This makes the sea level near the equator slightly higher than in the middle latitudes, creating a gentle gradient that causes water to flow down the slope.
- Wind: Wind blowing over the ocean surface exerts a frictional drag, pushing the water and initiating its movement in the direction of the wind.
- Gravity: Gravity acts on the gradient created by solar heating and the piling up of water by wind. It tends to pull the water down the slope, contributing to its flow.
- Coriolis Force: Caused by the Earth's rotation, the Coriolis force deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflection is crucial in forming large circular currents known as gyres.
Additionally, differences in water density, caused by variations in temperature and salinity, also drive currents. Denser (colder, saltier) water sinks and moves along the ocean floor, while less dense (warmer, less salty) water rises, creating vertical circulation.
Q1Project Work
(i) Visit a lake or a pond and observe the movement of waves. Throw a stone and notice how waves are generated.
Solution
This project requires a practical observation. Upon visiting a pond or lake and throwing a stone into the water, you should observe the following:
- Generation of Waves: The impact of the stone displaces the water at the point of entry. This disturbance creates energy that radiates outwards in the form of concentric circles, which are the waves or ripples.
- Movement of Energy, Not Water: If you place a small leaf or twig on the water's surface, you will notice that as the waves pass, the object mostly bobs up and down in the same location. It does not travel outwards with the wave. This demonstrates the key concept from the chapter: waves are the transfer of energy through the water, while the water particles themselves only move in a small circular or orbital motion.
Q2Project Work
(ii) Take a globe and a map showing the currents of the oceans. Discuss why certain currents are warm or cold and why they deflect in certain places and examine the reasons.
Solution
This activity involves analyzing a map of ocean currents (like Figure 13.3 in the chapter) to understand their characteristics and movements. Your discussion should cover the following points:
-
Warm and Cold Currents: Identify major currents and classify them. You will notice that warm currents (e.g., Gulf Stream, Kuroshio Current) generally originate in the low latitudes near the equator and flow towards the poles. They carry warm tropical water to higher latitudes. Conversely, cold currents (e.g., Canary Current, California Current, Labrador Current) originate in high latitudes near the poles and flow towards the equator, carrying cold polar water to lower latitudes.
-
Deflection of Currents: Observe the paths of the currents. You will see that they do not flow in straight lines. For example, currents in the Northern Hemisphere tend to bend to the right, while those in the Southern Hemisphere bend to the left. This deflection is caused by the Coriolis force, which results from the Earth's rotation. This force is responsible for creating large, circular patterns of currents in the ocean basins, known as gyres.