Class - 6, Science, Chapter:- 14 (Water) Notes, NCERT Solutions & Frequently Asked Questions

 Science

Class:-6, Chapter:- 14

(Water)

Notes, NCERT Solutions & Frequently Asked Questions

-- Notes --

⭐ Water:- Water is precious, fundamental and the most essential substances required for the existence of life on earth. 

• Water is found naturally, abundantly on our planet earth. 

• About two-thirds of the total earth’s surface is covered with water. 

• It is a transparent, odourless and tasteless inorganic molecule composed of hydrogen and oxygen.

⭐ Uses of Water:- We all use water for different purposes, which includes everyday household uses, including drinking, cooking, cleaning, washing, bathing for other domestic, irrigating, cultivating the crops and industrial requirements. Thus, water is required for many activities.

⭐ Sources of water:- As mentioned above, about two-thirds (71 %) of the total earth’s surface is covered without water, but unfortunately, only a small percentage (2 to 3 per cent) is suitable for human use. 

• The other 99.7 per cent available water are found in oceans, sea, groundwater, floating in the atmosphere and in icecaps. 

• This water is not safe and is unsuitable for human consumption, as it consists excess salt, toxins and other impurities, which can lead to illness and other health disorders.

• Rivers, ponds, lakes and groundwater are the different sources of water, which can be used for drinking, cooking and other human uses only after proper treatment like boiling, filtering, etc.

⭐ Origin of water:- The origin of the water is found out to be from a type of meteorite.

• The major sources of water for human use are lakes, rivers, ponds etc.

• The chemical composition of water on earth is the same as that of some meteorites.

⭐ Freshwater:- Freshwater is a naturally occurring water present on the earth’s surface in ponds, rivers. 

⭐ Distribution Of Freshwater:- 

a) Freshwater VS Saltwater:- 71% of Earth is filled with water, out of this 3% is fresh water and 97% of water is in oceans and seas. 

• Out of this 3% of freshwater, 30% is groundwater(not accessible), 69% are in the form glaciers, icebergs. ( not accessible).

• Out of the remaining 1% of water, only 0.006% is used by the people for several purposes like bathing, washing.

b) Potable water:- The pure form of water, which does not contain any impurities or salts in it and can be used for drinking purposes is called potable water.

c) Water from oceans:- Out of 71% of the water on earth, 97% is the water from oceans and seas. Water from oceans and seas contains dissolved salts in it, hence this water is called saltwater or saline water.

⭐ Water Cycle:- The process of circulating or the continuous movement of water between water bodies like the ocean, rivers, ponds, lakes and atmosphere is called the water cycle. 

• It is also also known as the hydrologic cycle or the hydrological cycle. 

• In this process, the water on the earth changes into three different states of matter – solid, liquid and gas. 

• The complete process of the water cycle involves the following process.

a) Evaporation:- Evaporation is the process of converting liquid or water into the gaseous form or vapour state.

b) Condensation:- The process of converting vapour or gaseous form into its liquid form is called condensation.

• Water collected on the surface of water bottle is due to the condensation. 

c) Precipitation:- When more water gets condensed in clouds or condensation of water vapour in the atmosphere results in precipitation. The precipitation can be in the form of rain, snow, hail.

⭐ Flow of water towards the oceans:- Rainwater falls into rivers, lakes etc.

• The rain droplets fall into oceans, rivers, ponds, seas.

• Water from the rivers, lakes, ponds finally flow into the sea and ocean.

⭐ Transpiration:- In plants, the process of evaporating water through leaves when water is absorbed through roots is called transpiration.

⭐ Flood:- Rainfall brings about life but excess rainfall leads to an increase in water level in water bodies like rivers, ponds.

• This excess water may spread over large areas causing floods.

⭐ Adverse effects of floods:- Flood causes damages to human life, crops, domestic animals and animals living in the water.

⭐ Drought:- Inadequate rainfall leads to a decrease in groundwater level which makes soil dry. This condition is called drought.

• At the time of drought, it is difficult to get food and water.

⭐ Ground Water:- The water present underground or beneath the earth’s surface in spaces of soil and rocks are called groundwater.

⭐ Water level:- Level of water or it is the height reached by the water in lakes, ponds, storage tanks, dams.

⭐ Infiltration:- The process of water seeping into the soil after falling onto the surface of the ground is called infiltration.

⭐ Water Management:- Water management is the effective utilisation of water or managing the water resources carefully. Water can be managed in the following ways:-

a) Drip Irrigation:- The process of pouring water to the roots of plants using narrow tubes is called Drip Irrigation.

b) Rainwater Harvesting:- Collection of rainwater and using it effectively for other purposes is known as rainwater harvesting.

-- NCERT Solutions --

Question 1.- Fill Up The Blanks In The Following:-

a) The process of changing water into its vapour is called ______.

b) The process of changing water vapour into water is called ________.

c) No rainfall for a year or more may lead to ______ in that region

d) Excessive rains may cause_______.

Solution:- 

a) Evaporation

b) Condensation

c) Draught

d) Floods

Question 2.- State for each of the following whether it is due to evaporation or condensation:-

a) Water drops appear on the outer surface of a glass containing cold water.

b) Steam rising from wet clothes while they are ironed.

c) Fog appearing on a cold winter morning. 

d) Blackboard dries up after wiping it.

e) Steam rising from a hot girdle when water is sprinkled on it.

Solution:- 

a) Condensation

b) Evaporation

c) Condensation

d) Evaporation

e) Evaporation

Question 3.- Which of the following statements are "true"?

a) Water vapour is present in the air only during the monsoon.

b) Water evaporates into the air from oceans, rivers and lakes but not from 

c) The process of water changing into its vapour is called evaporation.

d) The evaporation of water takes place only in sunlight.

e) Water vapour condenses to form tiny water droplets of water in the upper layers of air where it is cooler.

Solution:- 

a) False

b) False

c) True

d) False

e) True

Question 4.- Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how?

Solution:- Yes, to dry school uniform quickly, spreading it near an anghiti or heater will help. Anghiti or heater provides heat which increases the evaporation rate and as a result, the school uniform dries quickly.

Question 5.- Take out a cooled bottle of water from the refrigerator and keep it on a table. After some time, you notice a puddle of water around it. Why?

Solution:- We see a pool of water after a while when we take a cooled bottle of water from the refrigerator and place it on a table. This happens due to the condensation process. The water vapour condenses out due to low temperature around the bottle and droplets of water are seen.

Question 6.- To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet?

Solution:- The glasses become wet due to the breath because of condensation. The air which we breathe out contains carbon dioxide and moisture which condense due to lower temperature and wet the glass.

Question 7.- How are clouds formed?

Solution:- The water present on the earth forms water vapour because of evaporation. The water vapour then mixes with the air which due to an increase in the temperature, takes the water vapour in the upward direction. At higher altitudes, the temperature of the water vapour decreases which on cooling forms water droplets in the air referred to as clouds.

Question 8.- When does a drought occur?

Solution:- Drought is a phenomenon that occurs due to the scarcity of rainwater. It occurs in places that lack rainfall. As a result, underground water is not restored and soil loses its moisture due to evaporation.

-- Frequently Asked Questions --

Question 1.- What are the main reasons for ‘Water pollution’?

Solution:- Rapid urban development 2. Improper sewage disposal 3. Oil spills 4. Chemical waste dumping 5. Radioactive waste discharge

Question 2.- What is a ‘Freshwater lake’?

Solution:- A freshwater lake contains water that is not salty, usually in contrast to the sea.

Question 3.- What are the steps involved in the ‘Water cycle’ of nature?

Solution:- 

1. Evaporation

2. Condensation

3. Precipitation