Ans. There are three different zones of a flame – innermost zone (dark zone), middle zone (luminous zone) and outer zone non-luminous zone.
Ans. A chemical process in which a substance reacts with oxygen to give off heat is called combustion. Example: Burning of charcoal.
Ans. Food is called fuel for our body because in our body food is broken down by reaction with oxygen and heat is produced.
Ans. The innermost zone of a flame is black in colour due to presence of unburnt vapours of the combustible material.
Ans. CO2, being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled.
Ans. For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide (CO2) is the best extinguisher.
Ans. Water is not used to control fires involving electrical equipment because water may conduct electricity and harm those trying to douse the fire.
Ans. The harmful products released by the burning of fuels are unburnt carbon particles, carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen oxides etc.
Ans. The combustion that takes place rapidly and produces heat and light is called rapid combustion. Example: Gas burns rapidly and produces heat and light.
Ans. Water is heavier than oil. So, it sinks below the oil, and oil keeps burning on top. Thus, water is also not suitable for fires involving oil and petrol.
Ans. Combustion of most fuels releases carbon dioxide in the environment. Increased concentration of carbon dioxide in the air is believed to cause global warming.
Ans. Global warming results in the melting of polar glaciers, which leads to a rise in the sea level, causing floods in the coastal areas. Low lying coastal areas may even be permanently submerged under water.
Ans. The substance that undergoes combustion is said to be combustible substance. Some of the combustible substances are wood, coal, charcoal, paper, dry leaves, petrol etc.
Ans. The substance that does not burn is said to be non-combustible substance. Some of the non-combustible substances are soil, stone, glass, water etc.
Ans. The ignition temperature of a piece of wood is high which cannot be reached by the small heat produced by a burning matchstick. So, a matchstick cannot light (or burn) a piece of wood directly.
Ans. During hot summers, sometimes the ignition temperature of dry grass in the forest is reached, which makes the dry grass catch fire. From grasses, it spreads to trees, and very soon the whole forest is on fire.
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