Flame

Objective 

This topic gives an overview of; 

  • Flame
  • Structure of Flame

Flame

A hot glowing body of ignited gas that is generated by something on fire is called FlameKerosene oil and molten wax are substances that give a flame while burning.Wood and charcoal are substances that do not vaporise, but still burn, without any flame.

Observe an LPG flame. Can you tell the colour of the flame. 

Recall your experience of burning a magnesium ribbon in previous classes. Record your observations and mention whether on burning the material forms a flame or not.

Materials forming Flame on Burning

S.No. Material Forms flame Does not form flame
1 Candle  Forms flame  
2 Magnesium    Does not form flame
3 Camphor Forms flame  
4 Kerosene Stove Forms flame  
5 Charcoal Forms flame  

Structure of a Flame

Light a candle (Caution : Be careful). Hold a glass tube with a pair of tongs and introduce its one end in the dark zone of a non-flickering candle flame. Bring a lighted matchstick near the other end of the glass tube. You will see the flame. Notice that the wax near the heated wick melts quickly.

The substances which vapourise during burning, give flames. For example, kerosene oil and molten wax rise through the wick and are vapourised during burning and form flames. Charcoal, on the other hand, does not vapourise and so does not produce a flame. In the above activity, The vapours of wax coming out of the glass tube could  be the cause of the flame produced.

When the candle flame is steady, introduce a clean glass plate/slide into the luminous zone of the flame . Hold it there with a pair of tongs for about 10 seconds. Then remove it. 

A circular blackish ring is formed on the glass plate/slide. It indicates the deposition of unburnt carbon particles present in the luminous zone of the flame. Hold a thin long copper wire just inside the flame for about 30 seconds.

 

Notice that the portion of the copper wire just outside the flame gets red hot. It indicate that the non-luminous zone of the flame has a high temperature. In fact, this part of the flame is the hottest part.

Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for melting gold and silver . They use the outermost zone of the flame.

 

There are several "zones" within a non-luminous flame, and each zone has a different temperature. The outermost zone of the flame is blue in colour and it is the hottest part. This is due to complete combustion. The middle zone is moderately hot and is yellow in colour. This is because of partial combustion. The innermost zone is the least hot and black in colour. This is due to the presence of unburned wax vapours.

Summary

  • A hot glowing body of ignited gas that is generated by something on fire is called Flame
  • Fire can be controlled by removing one or more requirements essential for producing fire.
  • Water is commonly used to control fires.
  • Water cannot be used to control fires involving electrical equipments or oils.
  • There are three different zones of a flame - dark zone, luminous zone and non-luminous zone.

 

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