fuel and oxygen do not make fire by themselves.(change the voice)
Answers
Page No 118:
Question 1:
Mark the correct answer in each of the following.
(i) Early man was frightened of
(a) lightning and volcanoes.
(b) the damage caused by them.
(c) fire.
(ii)
(a) Fire is energy.
(b) Fire is heat and light.
(c) Fire is the result of a chemical reaction.
ANSWER:
(i) Early man was frightened of fire.
(ii) Fire is the result of a chemical reaction.
Page No 118:
Question 2:
From the boxes given below choose the one with the correct order of the following sentences.
(i) That is fire.
(ii) A chemical reaction takes place.
(iii) Energy in the form of heat and light is released.
(iv) Oxygen combines with carbon and hydrogen.
(i) (ii) (iii) (iv)
(ii) (iii) (i) (iv)
(iv) (iii) (ii) (i)
(iv) (ii) (iii) (i)
ANSWER:
(iv) (ii) (iii) (i)
Page No 119:
Question 1:
What do you understand by the ‘flash point’ of a fuel?
ANSWER:
The temperature at which a fuel begins to burn is called its flash point.
Page No 119:
Question 2:
(i) What are some common uses of fire?
(ii) In what sense is it a “bad master”?
ANSWER:
(i) Some of the common uses of fire are to cook food, warm the homes in winter and to generate electricity.
(ii) It is a “bad master” because if it is not kept under control, it can prove very dangerous. Each year thousands of homes and shops are damaged by fire. Vast areas of forest are also destroyed and hundreds of people are killed or injured.
Page No 119:
Question 3:
Match items in Column A with those in Column B.
A
B
(i)
(ii)
(iii)
fuel
oxygen
heat
-
-
-
-
-
-
-
lighted matchstick
air
coal
burning coal
wood
smouldering paper
cooking gas
ANSWER:
A
B
(i)
(ii)
(iii)
fuel
oxygen
heat
-
-
-
coal, wood, cooking gas
air
lighted matchstick, burning coal, smouldering paper
Page No 119:
Question 4:
What are the three main ways in which a fire can be controlled or put out?
ANSWER:
Fire can be controlled or put out by taking away one of the three things required for burning.
The first way is to take away the fuel. If the fire has no fuel to feed on, no burning can take place.
The second way is to prevent oxygen from reaching it. Small fires can be put out with a damp blanket or a sack. This stops oxygen from reaching the burning material. Sometimes carbon dioxide is used for extinguishing fire.
The third way of putting out a fire is to remove the heat. If the temperature can be brought down below the flash point, the fuel stops burning. Blowing on a burning matchstick or a candle removes the hot air around the flame, bringing down its temperature below the flash point. Sometimes water is sprayed on a fire. It absorbs heat from the burning fuel and lowers the temperature. It also cuts off the supply of oxygen, and therefore, fire is extinguished.
Answer:
Oxygen comes from the air. That is why when you blow on smouldering paper, it often bursts into flame. Fuel and oxygen do not make a fire by themselves. It only means that fire is very useful.