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Changes Around Us: Physical and Chemical — Science STD 7 — Question

Gujarat BoardEnglish MediumSTD 7ScienceChanges Around Us: Physical and Chemical3 Marks
✓

Answer

Observation and conclusion: The substance catches fire only when its ignition temperature is reached. Ignition temperature is the minimum temperature at which the substance catches fire. When a lighted matchstick is brought near to the paper it catches fire immediately because the temperature of the matchstick is already higher that the ignition temperature of the paper. In another case, when sunrays are focused using a magnifying glass on a piece of paper, it gets heated up and the temperature of paper increases and it attains its ignition temperature and starts burning and emit smoke.
Requirements for combustion process to occur :
1. A combustible substance (fuel)
2. Oxygen
3. Attainment of ignition temperature.

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