Class 7 Geography
Question 1: Describe tides.
Answer: The rhythmic rise and fall of water twice in a day is called a tide. A high tide occurs when water covers much of the shore by rising to its highest level. A low tide occurs when water falls to its lowest level and recedes from the shore.
Tides are caused by the strong gravitational pull exerted by the sun and the moon on the earth’s surface. The rise and fall of water due to tides is used for generating electricity in some places. The water of the earth closer to the moon gets pulled under the moon’s gravitational force and causes a high tide.
Question 2: What are waves?
Answer: When the water on the surface of the ocean rises and falls alternately, they are called waves. They are formed when winds scrape the ocean floor. The stronger the wind blows, the bigger the wave becomes. During a storm, the wind blows at a very high speed forming huge waves. These may cause tremendous destruction.
Question 3: What are ocean currents?
Answer: They are streams of water flowing continuously on the ocean’s surface in definite directions. They influence the temperature conditions of the area. They may be warm or cold. Warm currents originate near the equator and move towards the poles. The Gulf Stream is a warm current. They bring about warm temperature over land surface. Cold currents carry water from polar or higher latitudes to tropical or lower latitudes. For example, the Labrador Ocean current. They result in cold temperature over the land surface.
Question 1: Define waves.
Answer: It is the alternate rise and fall of water on the surface of the ocean.
Question 2: Name the sources of saline water.
Answer: Oceans and seas.
Question 3: Define salinity.
Answer: It is the amount of salt in grams present in 1000 grams of water.
Question 4: Define terrarium.
Answer: It is the artificial enclosure for keeping small house plants.
Question 5: Give examples of areas where warm and cold currents meet?
Answer: The seas around Japan and the eastern coast of North America.
Question 1: Write a note on the distribution of water bodies.
Answer: Three–fourths of the earth’s surface is covered by water. About 97% of total water on earth is in oceans and seas. About 3% of total water on earth is in the form of freshwater. About 2% of total water on earth is available as frozen ice in ice caps and glaciers. So, less than 1% of total water on earth is available for human usage.
Question 2: What is ocean circulation?
Answer: Unlike the calm waters of a pond or lakes, ocean water keeps moving continuously. This movement is called ocean circulation. These movements can be classified into –waves, tides and currents.
Question 3: What are the types of tides?
Answer: Tides are of the following types:
Question 4: What are the benefits of high tides?
Answer: They help in navigation by raising the water level close to the shores and help the ships to arrive at the harbor more easily. They help in fishing. More fish come closer to the shore during high tides. This helps the fishermen to have a good catch and earn more.
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