Question

1. List conditions under which combustion can take place.
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
3. Explain how the use of CNG in automobiles has reduced pollution in
our cities.
4. Compare LPG and wood as fuels.
5. 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.
6. Make a labelled diagram of a candle flame.
7. Name the unit in which the calorific value of a fuel is expressed.
8. Explain how CO, is able to control fires.
9. It is difficult to burn a heap of green leaves but dry leaves catch fire easily.
Explain.
10. Which zone of a flame does a goldsmith use for melting gold and silver
and why?
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.
12. Can the process of rusting be called combustion? Discuss.
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?​

Answer 1

1.The conditions under which combustion takes place are as follows:-

Presence of combustible substance.

Presence of supporter of combustion i.e., oxygen.

Attainment of ignition temperature. (The lowest temperature at which a substance catches fire is called its ignition temperature).

2.(a) Burning of wood and coal causes pollution of air.

(b) A liquid fuel, used in homes is Liquefied Petroleum Gas (LPG).

(c) Fuel must be heated to its Ignition temperature before it starts burning.

(d) Fire produced by oil cannot be controlled by water.

3.

Answer 2

Answer:

1. (a) Presence of fuel

(b) oxygen

(c) ignition temperature

2 (a) pollution

3.(b) L.P.G

(c) ignition temperature

(d) water