Science · Class 8
Combustion and Flame
Fuel, ignition temperature, types of combustion, and fire safety.
4 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Combustion is reaction with oxygen releasing heat and light. This chapter covers types of combustion, structure of flame, fuel efficiency, calorific value, and fire safety.
Combustion Basics
- Fuel + oxygen → combustion products + heat
- Ignition temperature: minimum temp to burn
- Inflammable substances have low ignition temp (petrol, LPG)
Structure of Flame
- Non-luminous zone: hottest, complete combustion (blue)
- Luminous zone: incomplete combustion, glowing carbon (yellow)
- Outer zone: complete combustion
Fuel Efficiency
- Calorific value: heat on complete combustion of 1 kg fuel (kJ/kg)
- LPG high calorific value; cow dung lower
- CNG cleaner — less soot
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Fire triangle
What three things are needed for fire?
- 1Fuel, oxygen (air), heat/ignition temp
- 2Remove any one — fire extinguishes
- 3Blanket cuts oxygen
Answer
Fuel, oxygen, and heat
Flame zones
Which part of candle flame is hottest?
- 1Outer non-luminous blue zone
- 2Complete combustion
- 3Hottest part — use for heating
Answer
Outer zone
Key Points to Remember
- ✓ Water extinguishes ordinary fires not oil/electrical
- ✓ CO₂ fire extinguisher cuts oxygen supply
- ✓ Forest fires spread by wind
Exam Tips
- • Draw labelled candle flame
- • Define ignition temperature
- • Compare calorific values of fuels
Practice MCQs — Combustion and Flame
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Combustion needs: