Ch 6 explains combustion (burning), conditions required, types of combustion, the structure of a flame, and how different fuels compare in efficiency (calorific value).
Combustion: a chemical process where a substance reacts with O₂ to give heat and light. Conditions: combustible substance (fuel), air (O₂), ignition temperature (minimum temperature to catch fire). Types: rapid (wood burning), spontaneous (no external heat needed — white phosphorus), explosion (very fast with gas production — firecrackers).
A flame has three zones: dark zone (unburnt gases, lowest temp), luminous zone (partial burning, yellow, moderate temp), non-luminous zone (complete burning, blue, hottest). Calorific value = heat produced by burning 1 kg of fuel. LPG and CNG have high calorific values; wood has low.
Download: https://ncert.nic.in/textbook/pdf/hesc106.pdf | Complete book: https://ncert.nic.in/textbook/pdf/hesc1ps.zip
Water cools the burning material below its ignition temperature and also cuts off oxygen supply by forming a layer. However, water should NOT be used on electrical or oil fires — it can spread the fire or cause electrocution.
Book a Trial + Diagnostic session. Get a personalized Learning Path with clear milestones, tutor match, and a plan recommendation — all within 24 hours.
Book Trial + Diagnostic →