Wednesday, September 19, 2012

CBSE Class 6 - Science - CH14 - Water

Water
One can live only about 1 week
without water
NCERT Chapter Solutions, MCQs, Q & A

Q1: Fill up the blanks in the following:

(a) The process of changing of 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 _________________.
(e) Water disappears from wet clothes by the process of ___________________.
(f) In winter mornings , __________is formed due to condensation of water vapour near the ground.
(g) The major natural source of water is _________________.
(h) Many tiny water droplets high up in the air, come together and fall down as _____________, __________ and ___________.

Answer:


(a) evaporation
(b) condensation
(c) drought
(d) flood
(e) evaporation
(f) fog
(g) oceans and sea
(h) rain, hail, snow


Q2: 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.

Answer:
(a) Water drops appear on the outer surface of a glass containing cold water. - condensation
(b) Steam rising from wet clothes while they are ironed. - evaporation
(c) Fog appearing on a cold winter morning. - condensation
(d) Blackboard dries up after wiping it. - evaporation
(e) Steam rising from a hot girdle when water is sprinkled on it. - evaporation



Q3: Which of the following statements are “true” ?

Answer:
(a) Water vapour is present in air only during the monsoon. (False ✗)
(b) Water evaporates into air from oceans, rivers and lakes but not from the soil.(False ✗)
(c) The process of water changing into its vapour, is called evaporation.(True ✓)
(d) The evaporation of water takes place only in sunlight.(False ✗)
(e) Water vapour condenses to form tiny droplets of water in the upper layers of air where it is cooler.(True ✓)
(f) Life is possible on earth without water (False ✗)
(g) When water is heated, it changes into ice. (False ✗)
(h) Evaporation of water takes place at all times. (True ✓)
(i) Saline water is fit for drinking and other domestic, agricultural and industrial needs. (False ✗)
(j) About two-thirds of the earth is covered with water. (True ✓)




Q4: Suppose you want to dry your school uniform quickly. Would spreading it near an anghiti or heater help? If yes, how?

Answer: Yes, spreading school uniform near anghiti or heater would help dry it quickly. Heater will warm up the surroundings and increase the rate of evaporation. Therefore school uniform will dry up quickly.


Q5: Take out a cooled bottle of water from refrigerator and keep it on a table. After some time you notice a puddle of water around it. Why?

Answer: It is due to condensation of water vapours present in air.  The cold surface of the bottle cools the air around it, and the water vapour of the air condenses on its surface.


Q6: To clean their spectacles, people often breathe out on glasses to make them wet. Explain why the glasses become wet.

Answer: When we breathe out, moist air comes out which make the glasses wet. Also when we breathe out, we release carbon-dioxide gas which cools the surroundings by absorbing heat from air, thus condenses the water vapours.


Q7: How are clouds formed?

Answer: Clouds are formed due to the process of evaporation and condensation. When air moves up, it gets cooler and cooler. At sufficient height, the air becomes so cool that water vapours present in the air condense. They form tiny droplets and float in air as clouds.


drought
Drought
credits:wikipedia
Q8: When does a drought occur?

Answer:  When there is insufficient or no rainfall occurs for more than a year in a region, the scarcity of water happens. Ponds and wells dry up. The soil continues to lose water due to evaporation and transpiration and eventually dry. This leads to drought.


Q9: What is rainwater harvesting? What are the two rainwater harvesting techniques?

Answer: Collecting rain water and storing it for later use is called rainwater harvesting. The two techniques of rainwater harvesting are:
  1. Rooftop rainwater harvesting.
  2. Allowing water to into ground directly through roadside drains.


Q10: Explain Water cycle with diagram.

Answer: The continuous journey of water in nature from earth to clouds and back to the earth is called water cycle.  The water cycle mainly consists of following processes:
  • Evaporation and Transpiration
  • Condensation
  • Precipitation
  • Accumulation

  1. When the sun heats up the water in rivers, ponds, oceans and lakes, it turns water into vapours.  Plants also lose water into air due to transpiration.
  2. At sufficient heights, the water vapours in the air cool down and condense to form clouds
  3. Precipitation occurs when too much water vapours condense. The clouds become heavy and begin to fall as rain, hail or snow.
  4. The water falls on the earth, it goes into lakes, oceans, rivers and ground.

Q11: Explain how floods causes extensive damage to human life and property?

Answer:
  1. Droughts results in drying up of the crops and vegetation.
  2. Its leads to scarcity of food and fodder for humans and animal life.
  3. It leads to malnutrition in humans and animals.


Q12(MCQ): What do we see on the surface of the glass containing ice-chilled water ?

(a) dust
(b) water vapour
(c) water droplets
(d) ice

Answer: (c) water droplets

Q13(MCQ): Evaporation of water in shade is

(a) fast
(b) faster
(c) slow
(d) none of these

Answer:  (b) faster

Q14(MCQ): The process of changing water into water vapours is called

(a) filtration
(b) condensation
(c) evaporation
(d) sedimentation

Answer: (c) evaporation

Q15(MCQ): How much water is consumed by a city-dweller in washing, bathing, flushing the toilet etc.?

(a) 2-3 litres
(b) 10-15 litres
(c) 100-300 litres
(d) 1000-1500 litres

Answer:  (c) 100-300 litres

Q16(MCQ): If tap of your bathroom is leaking drop by drop, how much water is lost per day?

(a) 1 bucket full of water
(b) 2 buckets full of water
(c) 8 buckets full of water
(d) 20 buckets full of water

Answer:  (c) 8 buckets full of water


(In progress...)

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