Class VII

Ch 5 – Water surrounding the earth

QUESTIONS AND ANSWERS

D.

Q.1 On what factors does the height of wave depend?

Ans.1 The height of the waves depends on the speed of wind and the duration  of wind blowing from a particular direction.

Q.2 Define an ocean current?

Ans.2 The Ocean current is the continuous movement of a mass of water in a particular direction. Ocean currents are broadly of two types, i.e. cold currents and warm currents.

Q.3 How are tides caused?

Ans.3 Tides are the periodic rise and fall in the level of ocean water. They are caused due to gravitational pull of the moon and the sun. Tides occur twice a day.

Q.4 Name the important components of water cycle.

Ans.4.1. Condensation

          2. Evaporation

          3. Precipitation

Q.5 Name the valuable resources which are found in abundance in the ocean?

Ans. 5  a.  Mineral oil   

            b. Gold   

            c. Platinum

          d. Nickel

       e. Copper

E.

Q.1 How are tides useful to us?

Ans.1 Tides are useful to us in the following ways-

a)   High tides enables big ships to enter the harbour or sail out of the harbour

b)   Tidal energy is harnessed to generate electricity in the coastal areas.

c)   Tidal energy is one of the important renewable sources of energy

Q.2 How are oceans beneficial to us in improving the quality of life?

Ans.1.

1. The Ocean facilitates countries and regions to trade with one another.

2. Good can be moved in a very large quantity by ships and the             transportation is cheaper than any other mode of transport.

3. The marine environment provides animal and plant life for food and trade in abundance.

4. Some of the valuable mineral resources are found in the ocean floor. Mineral oil, manganese nodules, gold, platinum, nickel, copper and cobalt.

5. Several countries are tapping mineral oils as a source of energy in a big way.

Q.3 Explain the water cycle with the help of a diagram.

Ans.3.

1. The sun is the main source of energy which causes water to evaporate.

2. Hence water of the oceans is converted into water vapours due to the heat of the sun by the process of evaporation.

3. The evaporated vapours rise up in atmosphere and condense into tiny crystals of ice or droplets of water to form clouds. 

4. When the condensed ice crystals or water droplets grow in size and are unable to float, they fall down over the earth’s surface as precipitation. 5. It is because of the never ending circulation that process is described as water cycle.

( diagram on pg no. 33)

Q.4 Explain three effects of ocean currents.

Ans.4.

1. The ocean currents play an important role in influencing the climate of the coastal regions of the continents. If a warm current passes along the coast, it raises temperature and makes the place warmer than the surrounding areas. Similarly, cold currents make the adjoining coastal region colder.

2. The confluence of warm and cold currents provides ideal conditions for plentiful growth of plankton, which is a food for marine life. These areas serve as major fishing grounds, encouraging trade and commerce.

3. The ocean currents also help in navigation.

Q.5 Suggest four ways to help people affected by devastation due to tsunami.

Ans. 5.1. Government agencies, non-governmental organisations (NGOs) and residential welfare association, business organisations, shopkeepers, schools and colleges provided relief to the victims by donating money, clothes, medicines, beddings, tents etc.

2. Media played an important role in mobilising public help for the victims.

3. We can also volunteer in the affected areas.

4. Counselling session and blood donating camps can be organised in the areas affected by tsunami.