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13. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

The outermost part of the flame is the hottest region of the flame. Hence, water kept near it will get heated faster i.e in shorter time. Therefore, the water in Ramesh's beaker will get heated in a shorter time.

12. Can the process of rusting be called combustion? Discuss.

No, it cannot be considered as combustion because in rusting no heat or light is produced and in combustion a substance reacts with oxygen or air and gives out energy in the form of heat or light

11. In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ.Calculate the calorific value of the fuel.

The calorific value of the fuel is the amount of heat produced by the complete combustion of 1 kg of fuel. Given, Heat produced by 4.5 kg of fuel  = 180000 kJ  Heat produced by 1 kg of fuel = 180,000 kJ/4.5 Kg = 40,000 kJ   The calorific value of the fuel is 40,000 kJ/kg.

10. Which zone of a flame does a goldsmith use for melting gold and silver and why?

The goldsmith uses the outermost non-luminous (blue) zone for melting gold and silver. This is because it is the hottest part of the flame and hence melts the metals easily.

9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

It is difficult to burn a heap of green leaves but dry leaves catch fire easily because green leaves have moisture present in them. Hence the heat gets absorbed by water to provide energy to evaporate. But, the dry leaves have no moisture and hence the heat is not lost. That is why it catches fire easily.

8. Explain how $CO_{2}$ is able to control fires.

is heavier than . Therefore, it acts as a blanket over the substance and cuts off the oxygen supply required for combustion. This way  is able to control fires.

7. Name the unit in which the calorific value of a fuel is expressed.

The calorific value of a fuel is expressed in kilojoules per kilogram (kJ/kg).

6. Make a labelled diagram of a candle flame.

Following is the labelled diagram of a candle flame:

5. Give reasons.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

Paper has a low ignition temperature and hence catches fire easily. But when it is wrapped around an aluminium pipe, heat is transferred to the metal and hence the ignition temperature of the paper is not reached. That is why paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

5. Give reasons.

(b) LPG is a better domestic fuel than wood.

Wood produces lots of smoke and unburnt carbon particles, which cause respiratory problems. But LPG does not produce these. Thats why LPG is a better domestic fuel than wood.

5. Give reasons.

(a) Water is not used to control fires involving electrical equipment.

Water is not used to control fires involving electrical equipment because water being a good conductor of electricity may lead the electric current to spread causing electric shocks or short-circuits.

4. Compare LPG and wood as fuels.

LPG Wood                     It does not produce smoke. It produces smoke. It is easy to store and can be easily transported using pipelines. It takes a lot of space to store. It has low ignition temperature It has a high ignition temperature It does not cause environmental pollution It leaves un-burnt carbon particles causing air pollution Calorific value is...

3. Explain how the use of CNG in automobiles has reduced pollution in our cities.

Fuels like petroleum and coal release toxic gases like carbon monoxide, carbon dioxide, and sulphur dioxide during combustion. These harmful gases cause pollution and respiratory problems. Whereas CNG (Compressed Natural gas) is a clean fuel and produces these harmful gases in very small quantity.  (CNG is methane stored at high pressure!)

2. Fill in the blanks.
(a) Burning of wood and coal causes_________ of air.
(b) A liquid fuel, used in homes is_________ .
(c) Fuel must be heated to its___________  ___________ before it starts burning.
(d) Fire produced by oil cannot be controlled by__________ .

(a) Burning of wood and coal causes pollution of air. (b) A liquid fuel, used in homes is LPG(Liquified Petroleum Gas) . (c) Fuel must be heated to its ignition temperature before it starts burning. (d) Fire produced by oil cannot be controlled by water .

1. List conditions under which combustion can take place.

The conditions required for the combustion to take place are: (a) Presence of oxygen (b) Presence of inflammable substance (fuel) (c) Maintain Ignition Temperature (the minimum temperature at which substance catches fire).

11. Complete the word puzzle

. Down

1. Species on the verge of extinction.

2. A book carrying information about endangered species.

5. Consequence of deforestation.

Across

1. Species which have vanished.

3. Species found only in a particular habitat.

4. Variety of plants, animals and microorganisms found in an area.

ENDANGERED & EXTINCT RED DATA BOOK ENDEMIC BIODIVERSITY DROUGHT

10. Why should paper be saved? Prepare a list of ways by which you can save paper.

The paper should be saved because to make one-tonne paper we need to cut approximately seventeen fully grown tree. Therefore, to save trees and prevent the impact of their loss on living organisms. we need to save the papers. Paper can be saved by following ways- by collecting used paper and recycle it use both sides of the paper  Spread the awareness about paper Use paper efficiently

9. Find out about national parks in your state. Identify and show their location on the outline map of India.

Name of the state- West Bengal National park- Sundarban nation park Here below the outline of Sundarban national park

8. Explain how deforestation leads to reduced rainfall.

Deforestation means the removal of trees or plants from an area for different purposes. We know that plants absorb carbon dioxide from the atmosphere. and if there is no plant, the level of carbon dioxide in the atmosphere will rise. These lead to increasing the temperature of the earth, and it will disturb the water cycle. As a result of the disruption in the water cycle, also affect the...

7. How can you contribute to the maintenance of green wealth of your locality? Make a list of actions to be taken by you.

We can contribute to the maintenance of green wealth of our locality by following ways- By taking cares of plants and trees of our surroundings. We can do more number of planting. To encourage the people of my area to plant more trees by telling them about the importantness of trees. We can aware the young children by telling them the consequences of deforestation and how they affect the...
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