CBSE Class 8 Answered

(a) The different types of flame produced depending on the proportion of oxygen available for burning of fuel are:

i. When the oxygen supply is sufficient, then the fuels burn completely producing mainly a blue flame. This blue flame does not produce much light, so it said to be a non-luminous flame. Example: In kitchen gas stoves, LPG burns with a blue flame.

ii. When the oxygen supply is insufficient, then the fuels burn incompletely producing mainly a yellow flame. This yellow flame produces light, so it said to be a luminous flame. Example: When kerosene is burned in a lamp, it burns with a yellow, luminous flame.

(b) Activity: Light a candle. Hold a clean glass plate with the help of a pair of tongs and introduce it in the middle zone of the candle flame. Hold the glass plate in this position for about 10 seconds. We will find that a blackish ring is formed on the glass plate. This blackish ring is produced due to deposition of unburnt carbon particles present in the luminous zone of the candle flame. This activity shows that the partial combustion of wax vapours in the middle zone produces unburnt carbon particles.