Flame - II

Substances which vapourise on burning produce flame.

For example, a candle burns with a flame.

If we look closely in the flame we can observe different colours.

According to that we can divide the whole flame into three zones.

This difference in colours occurs because of the difference in the extent of combustion in the zones.

In the outermost part of the flame, complete combustion occurs because of the availability of excess oxygen.

Partial combustion takes place in the middlemost zone due to limited availability of oxygen.

In the innermost zone, incomplete combustion occurs due to lack of oxygen.

Let us try to understand the parts of a flame and their properties by performing an activity

For that, we have to take two test tubes with equal amount of water in each of them.

And label them as test tube A and test tube B.

Now we take two burning candles and use them to heat the test tubes

Let us expose the test tube A to the luminous zone of the flame

That means to the middle zone of the candle

And we expose the test tube B to the outermost part of the flame

We observe some changes in these test tubes

We see that water in test tube B starts boiling.

Whereas water in test tube A does not start boiling.

We also observe that the bottom of test tube A becomes black

From this activity we can draw some conclusions

Water in test tube B has started boiling because it was placed in the outermost part of the flames

That means, the outermost part is the hottest part of the flame.

The water in test tube A did not come to a boil as fast as the water in test tube B;

This is because the test tube A was exposed to the luminous zone of the flame which is less hot due to partial or incomplete combustion.

Also, we notice that the bottom of test tube A becomes black

This indicates the deposition of unburnt carbon particles present in the luminous zone of the flame

Revision

Substance that vapourise while burning produces the flame

For example, combustion of kerosine oil produces flame

In the outermost part of the flame, complete combustion happens because of lot of oxygen

If we take two burning candles and using these will heat two test tubes

The result suggest that due to complete combustion in the outermost part of the flame, water is boiling in one test tube

Whereas the other test tube we see no change because of partial combustion in the innermost part of the flame

The end