GEOGRAPHY- CLASS-11: FUNDAMENTALS OF PHYSICAL GEOGRAPHY
CHAPTER-13
Movements of Ocean Water
1. Multiple Choice Questions
(i) Upward and downward movement of ocean water is known as the:
Answer: (a) Tide
Explanation:
Tides are the periodic rise and fall of ocean water caused mainly by the gravitational pull of the Moon and the Sun. They result in the upward (high tide) and downward (low tide) movement of sea water.
(ii) Spring tides are caused:
Answer: (a) As a result of the Moon and the Sun pulling the Earth gravitationally in the same direction.
Explanation:
Spring tides occur during the New Moon and Full Moon when the gravitational forces of the Moon and the Sun act together. This combined pull produces the highest high tides and the lowest low tides.
(iii) The distance between the Earth and the Moon is minimum when the Moon is in:
Answer: (b) Perigee
Explanation:
Perigee is the position where the Moon is closest to the Earth. At this time, the Moon's gravitational pull is strongest, resulting in higher-than-normal tides.
(iv) The Earth reaches its perihelion in:
Answer: (d) January
Explanation:
Perihelion is the point in the Earth's orbit where it is nearest to the Sun. The Earth reaches perihelion around 3rd January every year.
2. Answer the following questions in about 30 words.
(i) What are waves?
Answer:
Waves are rhythmic up-and-down movements of ocean water caused mainly by wind. They transfer energy from one place to another without transferring the water itself over long distances.
(ii) Where do waves in the ocean get their energy from?
Answer:
Ocean waves obtain their energy mainly from winds blowing over the sea surface. The stronger and longer the wind blows, the larger the waves become.
(iii) What are tides?
Answer:
Tides are the regular rise and fall of sea level caused by the gravitational attraction of the Moon and the Sun along with the rotation of the Earth.
(iv) How are tides caused?
Answer:
Tides are caused mainly by the gravitational pull of the Moon and, to a lesser extent, the Sun. The Earth's rotation also influences the timing and occurrence of tides.
(v) How are tides related to navigation?
Answer:
High tides raise the water level near coasts and ports, allowing large ships to enter and leave harbours safely. Therefore, tides are very important for navigation and port operations.
3. 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?
Answer:
Ocean currents play an important role in regulating the temperature of coastal regions. Warm ocean currents carry warm water from the tropical regions towards higher latitudes, increasing the temperature of nearby coastal areas. In contrast, cold ocean currents carry cold water from polar regions towards lower latitudes, reducing the temperature of adjacent coasts. Ocean currents also influence rainfall, fog and climate. In North-Western Europe, the North Atlantic Drift, which is an extension of the Gulf Stream, carries warm water from the tropical Atlantic Ocean. This warm current raises the temperature of countries such as the United Kingdom, Norway and western France. As a result, winters remain much milder than those of other regions situated at the same latitude. Many ports remain ice-free throughout the year, making navigation and trade possible. Thus, warm ocean currents have a strong moderating effect on the climate of North-Western Europe.
(ii) What are the causes of currents?
Answer:
Ocean currents are produced by several natural factors working together. The most important cause is the prevailing winds, which push the surface water and create surface currents. Differences in temperature and salinity produce variations in water density, causing deep ocean currents known as thermohaline circulation. The rotation of the Earth causes the Coriolis force, which deflects ocean currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The shape of the continents and the configuration of ocean basins also influence the direction of currents. Gravitational forces of the Moon and the Sun generate tidal currents. Seasonal changes and differences in atmospheric pressure further modify ocean circulation. The combined action of these factors forms a complex system of ocean currents that redistributes heat and influences the climate of the world.