Editing Content :: Admin Scraper

Chapter

Content type

Position

Value

63 We observe that the candle that was not covered (Fig. 5.6a) continues to burn, whereas the candle that was covered with a l glass tumbler (Fig. 5.6b) stops burning after some time. Why does i this happen? m Since the candle covered by the glass tumbler does not have h C a continuous supply of air, the ﬂame gets extinguished soon. n The component of air that supports combustion is oxygen. This a can be conﬁrmed by the presence of carbon dioxide in the glass a s tumbler inverted on the candle. How can you test the presence y of carbon dioxide gas? P You can test the carbon dioxide gas by adding a small amount s U of lime water in the petri dish. You will notice that it turns milky. n This carbon dioxide was formed by the carbon from the wax and o the oxygen from the air. In other words, oxygen is required for A s combustion. g a SCIENCE AND SOCIETY h C If a person’s clothes catch ﬁre, what is the best way to extinguish the ﬁre? Wrap a blanket or cloth around the person. This cuts oﬀ the supply of air, and the ﬁre gets extinguished. Caution —Synthetic blanket or cloth should never be used to put out a ﬁre, as these can melt and stick to the skin. FASCINATING FACTS Nature’s wonders: You might have seen some insects emitting light in a garden or a ﬁeld in late evenings. These insects are called ﬁreﬂies, and their light is produced by a chemical change. This type of light production (without heat) in living organisms is called bioluminescence. Fireflies Is the Presence of Air Enough for Combustion? We learnt above that combustible substances and oxygen are necessary for combustion. We also know that paper is a combustible substance, but we can keep it in the air for any length of time without it catching ﬁre. What else is needed to start combustion? Let us learn about this. Reprint 2026-27