science - combustion and flame

Class 8 - Science

Combustion and Flame

Q&A
Notes
Question:
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?
Answer:

The water in the Ramesh's beaker will heat up in a shorter time. This is because the outermost zone of a flame is the hottest zone, while the yellow zone (in which Abida had kept the beaker) is less hot.

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Questions and Answers


Combustion and Flame - Questions
1. 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?
Answer
2.

Make a labelled diagram of a candle flame.


Answer
3.

List conditions under which combustion can take place.


Answer
4. Explain how C02 is able to control fires.
Answer
5. It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer
6. 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.
Answer
7. Compare LPG and wood as fuels.
Answer
8. Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer
9. Name the unit in which the calorific value of a fuel is expressed.
Answer
10.

Give reasons.
(a) Water is not used to control fires involving electrical equipment.
(b) LPG is a better domestic fuel than wood.
(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.


Answer
11. Can the process of rusting be called combustion? Discuss.
Answer
12. Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer
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