Important Questions: Water | Social Studies (SST) Class 7 PDF Download

Q1: How are high tides important? [V. Imp.]
Ans: High tides are important for various reasons:

• They help in navigation
• The raise the water level close to the shores. This helps the ships to arrive at the harbour more easily.
• The high tides also help in fishing. Many more fish come closer to the shore during the high. This enables the fisherman to get a plentiful catch.
• The rise and fall of water due to tides is being used to generate electricity in some places.

Q2: What is flood tide and ebb tide?
Ans: The rise of sea level is called the flood tide and fall is called the ebb tide.

Q3: Write a brief note on Tsunami. [Imp.]
Ans: Tsunami is a Japanese word that means ‘harbour waves’ as the harbours get destroyed whenever there is tsunami. An earthquake, a volcanic eruption or underwater landslides can shift large amounts of ocean water. As a result tsunami occurs which may be as high as 15 m. The tsunami of 2004 is still in our mind. It caused huge death and destruction in the coastal areas of India. The Indira point in the Andaman and Nicobar Islands got submerged after the tsunami.

Q4: How do we classify ocean movements? Explain. [V. Imp.]
Ans: Ocean movements can be classified into waves, tides and currents.

• When the water on the surface of the ocean rises and falls alternately, they are called waves. Waves are formed when winds scrape across the ocean surface. The stronger the wind blows, the bigger the wave becomes.
• The rhythmic rise and fall of ocean water twice in a day is known as a tide. Tides may be high or low. It is high tide when water covers much of the shore by rising to its highest level. It is low tide when water falls to its lowest level and recedes from the shore. Tides are caused due to the strong gravitational pull exerted by the sun and moon on the earth’s surface. High tides help in navigation and fishing. The rise and fall of water due to tides is being used to generate electricity in some places.
• Ocean currents. These are streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm such as the Gulf Stream and cold such as the Labrador Ocean current. The areas where the warm and cold currents meet provide the best fishing ground of the world. For example, seas around Japan and the eastern Coast of North America.

Q5: Our unique planet earth is covered by different categories of water. Give the distribution of water in percentage.
Ans:  We all know that three fourth of the earth surface is covered by water. Water plays a major role on the earth surface for the survival of different modes of life. The different categories of the water according to their catchment area are-
Ocean 97%, ice caps 02.0%, ground water 0.68%, fresh water 0.009%, Inland seas and salt lakes 0.009%, atmosphere 0.0019%, rivers 0.0001%

Q6: Explain water cycle with a neat and labelled diagram. [V. Imp.]
Ans: The sun’s heat causes evaporation of water, flowing down to stream or drains into water vapour. When the water vapour cools down, it condenses and forms clouds. These clouds, when become too heavy to float, start falling on the land or sea in the form of rain, snow or sleet. Thus, the process by which water continuously changes its form and circulates between oceans, atmosphere and land is known as the water cycle.

Q7: How are spring and neap tides formed. [V. Imp.]
Ans: During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides. But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and earth resulting in low tides. These tides are called neap tides.

Q8: What are waves? Write a short note on it
Ans: Waves are the rise and fall of the water on the surface of the ocean. Waves are formed when winds scrape across the ocean surface. The stronger the wind blows, the bigger the wave becomes. During the storm, the winds blow at very high speed and therefore huge waves are formed. These waves are very strong, hence very destruction. They may cause huge devastation.

Q9: Write a note on the importance of water. [V. Imp.]
Ans: Water is life. Without water, we cannot think of life. Its scarcity may create numerous problems but its absence would definitely lead to non-existence of all the living beings on the earth. It is a precious resource of the nature. We drink water whenever we feel thirsty. We use water in numerous activities such as washing clothes, cleaning house floors, watering garden etc. Industries also need water for their functioning. Thus, water is very essential and therefore we must conserve it. Our careless use of water has created several problems. Whatever water is there, it is not of good quality. We should think about the ways of its conservation for our own sake.

Q10: Give an account of ocean currents. [Imp.]
Ans: Ocean currents are streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm or cold. The warm ocean currents originate near the equator and move towards the poles. The cold current carry water from polar or higher latitudes to tropical or lower latitudes. For example the Labrador Ocean current is cold current while the Gulf Stream is a warm current. The ocean current influence the temperature conditions of the area.
Warm currents bring about warm temperature over land surface. The areas where the warm and cold currents meet provide the best fishing grounds of the world. For example seas around Japan and the eastern coast of North America. The areas where a warm and cold current meet also experience foggy weather and therefore navigation becomes difficult.

Q11: Name the two types of current and its movement on earth.
Ans: Ocean currents are broadly of two types of warm and cold currents. The warm currents flow from low latitudes in tropical zones towards the high latitudes in the temperate and sub polar zones. The cold current flow from high latitudes to low latitudes.

Q12: Why ocean bodies and sea contain salty water?
Ans: Because it contains the large amount of dissolved salts. Most of the salt is sodium chloride.

Q13: How tides are formed?
Ans: Tides are periodic rise and fall in the level of water in seas and ocean caused by the attraction of the moon and the sun. Twice a day, about every 12 hours and 26 minutes, the sea level rise and it falls.

Q14: Define vertical distribution of sea water.
Ans: When surface water gets heated by sun, water evaporates and increases the concentration of salts. Surface water becomes denser sinks and sub surface water rises up. Thus, salinity of sea water causes vertical circulation.

Q15: Name the factors which are responsible for the movement of oceanic water?
Ans: The factors are:

• Winds
• Temperature
• Coriolis force
• Attraction of moon and sun depending upon its distances.