Question

Apurva covered a burning candle with a glass. What will happen to the burning candle?
A.It will extinguish immediately
B.It will burn for some time before being cut off
C.It will continue burning
D.Candle will melt

Answer 1

Hint:A flame needs three things to come into existence, namely a source of energy (like a spark or heat), a fuel (thing that will burn) and a source of oxygen. If any one of these necessary requirements are removed, the flame no longer burns and is cut off.

Complete step by step answer:
Fire can be said to be the rapid and energetic oxidation of a fuel. In a typical fire, the source of oxygen is generally the air in the atmosphere. The more easily a fuel can accept oxygen, the more flammable it is. The fuel, usually hydrocarbons, uses up oxygen from its surroundings and forms carbon dioxide and water. The water produced evaporates as water vapour as soon as it is formed due to the high temperature of the flame.
If the burning candle is covered with a glass, it will burn for some time and then it will cut off. As the candle is covered with the glass, the amount of oxygen available for the burning of the flame is limited. The oxygen inside the now closed system is used up completely and now turns to carbon dioxide. Carbon dioxide gas does not support combustion and as a result, the flame is cut off.

Thus, the correct answer is B.

Note:
We can also see the glass acting as a barrier between the fuel (candle) and the source of oxygen (air). Since there is a barrier between the two necessary requirements, the burning will no longer continue. This principle is used to put off fires and water also extinguishes fir with the same principle. Water smothers the fire as it creates a barrier between the oxygen source and the fuel source. It also imparts a cooling effect as some energy is used up to convert the liquid water into water vapours.