Chapter 6
Combustion and Flame
1. List conditions under which combustion can take place.
Ans.
The conditions under which combustion can take place are
(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 ______
Ans.
(a) pollution
(b) LPG
(c) ignition temperature
(d) water
3. Explain How the Use of CNG in Automobiles Has Reduced Pollution in Our Cities.
The use of CNG in automobiles has reduced pollution in our cities because it is a cleaner fuel and produce very less smoke and harmful substances.
4. Compare LPG and wood as fuels.
Ans.
The conditions under which combustion can take place are
- The presence of air or oxygen.
- The presence of fuel.
- Ignition temperature.
(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 ______
Ans.
(a) pollution
(b) LPG
(c) ignition temperature
(d) water
3. Explain How the Use of CNG in Automobiles Has Reduced Pollution in Our Cities.
The use of CNG in automobiles has reduced pollution in our cities because it is a cleaner fuel and produce very less smoke and harmful substances.
4. Compare LPG and wood as fuels.
5. Give reasons.
(a) Water is not used to control fires involving electrical equipment.
Ans.
Water is not used to control fires involving electrical equipment because water is a good conductor of electricity due to which the person can get electric shock.
(b) LPG is a better domestic fuel than wood.
Ans.
LPG is a better domestic fuel than wood because LPG causes less pollution and have high calorific value.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminum pipe does not.
Ans.
Paper wrapped around pipe does not catch fire easily because that paper transfer the heat to the aluminum pipe and will not get its ignition temperature.
6. Make a Labeled Diagram of a Candle Flame.
(a) Water is not used to control fires involving electrical equipment.
Ans.
Water is not used to control fires involving electrical equipment because water is a good conductor of electricity due to which the person can get electric shock.
(b) LPG is a better domestic fuel than wood.
Ans.
LPG is a better domestic fuel than wood because LPG causes less pollution and have high calorific value.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminum pipe does not.
Ans.
Paper wrapped around pipe does not catch fire easily because that paper transfer the heat to the aluminum pipe and will not get its ignition temperature.
6. Make a Labeled Diagram of a Candle Flame.
7. Name the Unit in Which the Calorific Value of a Fuel is Expressed.
Ans.
Calorific Value of a fuel is expressed in KJ/Kg.
8. Explain how CO2 is able to control fires.
Ans.
CO2 is heavier than oxygen and cover the fire like a blanket, which cut off the contact of oxygen and control the fire.
9. It is Difficult To Burn a Heap of Green Leaves, but Dry Leaves Catch Fire Easily. Explain.
Ans.
It is difficult to burn a heap of green leaves because the green leaves have moisture which increase the ignition temperature.
10. Which Zone of a Flame Does a Goldsmith Use for Melting Gold and Silver and Why?
Ans.
Goldsmith uses the outermost zone of a Flame for melting gold and silver because the outer most zone is the hottest part of flame.
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.
Ans.
Ans.
Calorific Value of a fuel is expressed in KJ/Kg.
8. Explain how CO2 is able to control fires.
Ans.
CO2 is heavier than oxygen and cover the fire like a blanket, which cut off the contact of oxygen and control the fire.
9. It is Difficult To Burn a Heap of Green Leaves, but Dry Leaves Catch Fire Easily. Explain.
Ans.
It is difficult to burn a heap of green leaves because the green leaves have moisture which increase the ignition temperature.
10. Which Zone of a Flame Does a Goldsmith Use for Melting Gold and Silver and Why?
Ans.
Goldsmith uses the outermost zone of a Flame for melting gold and silver because the outer most zone is the hottest part of flame.
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.
Ans.
12. Can the process of rusting be called combustion? Discuss.
Ans.
No, although oxide is formed in rusting yet there is no light is produced in the process of rusting.
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?
Ans.
The water placed in the outermost part of the flame will be heated in a short time since it is a non-luminous flame and is regarded as the hottest part of the flame. So Ramesh’s beaker will be heated first.
Ans.
No, although oxide is formed in rusting yet there is no light is produced in the process of rusting.
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?
Ans.
The water placed in the outermost part of the flame will be heated in a short time since it is a non-luminous flame and is regarded as the hottest part of the flame. So Ramesh’s beaker will be heated first.