a. i) State the principle which is used in fire
fighting.
in) Name any two premises where no one
should be allowed to take any burning
material.
ii) The flame of a burning candle goes off
when we blow over it strongly. Why?
(mention two reasons)
Answers
Answer:
A lit candle might seem simple, but it is actually an example of a multi-step process resulting in combustion—and the glowing flame you see. Combustion is the result of a chemical reaction in which oxygen gas reacts with the substance that is being burned. The combustible material in a candle—or its fuel—is the wax. But before the wax can become fuel it first needs to get hot enough. To start that heating process, you first need to light the wick with another source of fire, such as a match. As the wick burns down the heat of the flame melts the wax around the wick. Because the wick is absorbent it sucks the liquid wax into the wick and upward into the flame. Once the liquid wax gets hot enough, it then turns from a liquid into a gas. The hot gas then reacts with the oxygen from the air and is burned, creating the candle flame that we see. This means that the candle flame is actually created by the burning wax gas—or vapor—and not by the wick itself or the solid or even liquid wax.
After lighting a candle, it might flicker or sputter at first, but then it usually burns fairly steadily. As the heat of the wax vapor flame melts more of the solid wax it creates more fuel for the flame to burn. The candle will only go out once it runs out of wax or oxygen—or gets blown out. After a candle goes out you can actually see the wax vapor escaping as a stream of white smoke. If you hold a match into that smoke, the candle will catch fire again—without even touching the wick! Don't believe it? Then try this activity to see for yourself!
Materials
Adult helper
Several small, narrow, birthday candles
Matches or a lighter
Wet sand (or another non-flammable substance to hold your candles up—you could also use cake or a cupcake!)