Question

Give reasons for each of the following.
(a) Water is commonly used to put out a fire.
(b) Water should not be used to put out a fire caused by oil or petrol.
(c) The middle zone of flame is yellowish in colour.
(d) Carbon dioxide is used to put out a fire caused by petrol or kerosene.
(e) A goldsmith blows the outermost zone of a flame with a metallic blowpipe to melt
gold pieces.​

Answer 1

Answer:

1)yes because water is having cooling affect

2)

Answer 2

Answer:

(a) Water is commonly used to put out a fire.

⇒ The three essential requirements for ignition are:-

• Presence of a combustible substance
• The temperature must be higher than ignition temperature
• There must be oxygen

Water is cool in temperature and lowers down the temperature of the fuel, and puts out the fire.

(b) Water should not be used to put out a fire caused by oil or petrol.

⇒ We know that oil/petrol is a highly inflammable substance. We also know that oil is less dense than water and floats on it. If we use water to put a petrol related fire, the oil would float on it and spread, causing the fire to increase.

(c) The middle zone of flame is yellow in colour.

⇒ The middle zone is an area of partial combustion. Due to partial combustion, the middle zone of the flame is yellow in colour.

(d) Carbon dioxide is used to put out a fire caused by petrol or kerosene.

⇒ Carbon dioxide lowers down the temperature of the fuel and also covers the fuel like a blanket which cuts out the supply of oxygen. This puts out the fire.

(e) A goldsmith blows the outermost zone of a flame with a metallic blowpipe to melt the gold pieces.

⇒ The outermost zone of the flame is the hottest part of the flame. Its temperature is around 1300°C. Goldsmiths use a blowpipe to direct the outermost part of the flame on the gold ornaments. This melts the pieces properly and helps in giving a precise shape to the ornaments.

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