Long Answers - Combustion and Flame, Science, Class 8 PDF Download

LONG ANSWER TYPE QUESTIONS
 

Q. 1. Complete the following table:  

Combustible and Non-combustible Substances

Ans. Combustible and Non-combustible Substances 

Q. 2. What are the essential conditions for combustion? Explain with the help of an activity.
Ans. Take a candle. Light it and fix it on a table. Put a glass chimney over the candle and rest it on wooden blocks in such a way that air can enter the chimney. We see that candle remains lighted. Remove the blocks and let the chimney rest on the table. We see that the flame flickers and produces smoke. Now put a glass plate over the chimney. We see that flame goes off because air is not available. This activity shows that air is essential to burn a fuel at its ignition temperature.

Q. 3. Describe the history of the matchstick.
Ans. History of matchstick is about five thousand years old. The modern safety match was developed only about 200 years ago. A mixture of antimony trisulphide, potassium chlorate and white phosphorus with some glue and starch was applied on the head of a match made of suitable wood. When it struck against a rough surface, white phosphorus got ignited and combustion of matchstick started. These days red phosphorus is used in place of white phosphorus. 

 
Q. 4. Explain various types of combustion.
Ans. Types of Combustion:
(i) Rapid combustion: The process of combustion in which a fuel burns rapidly to produce more amount of heat and light is known as rapid combustion. For example burning of gas.  
(ii) Spontaneous combustion: The type of combustion in which a material suddenly burns to produce flame without the application of any cause is called spontaneous combustion.
(iii) Explosion: The combustion in which a sudden reaction takes place with the evolution of heat, light, sound and a large amount of gas, is called explosion. Ignition of cracker produces explosion.

Q. 5. Complete the following table.
                                         Materials forming Flame on Burning 

Ans.                                 Materials forming Flame on Burning

Q. 6. Write three examples of each type of fuel in tabular form.
Ans.

Q. 7. Make a table to show the calorific value of various fuels.
Ans. 

Q. 8. What is deforestation? Write its effect on environment.
Ans. Cutting of trees is called deforestation.
Effects: D eforestation is very harmful to the environment.
1. The annual rainfall is disturbed in that area.
2. The frequent floods come.
3. Balance of oxygen and carbon dioxide is disturbed.
4. It causes respiratory problem.
5. Trees provide us with useful substances which are lost due to deforestation.

Q. 9. What are the ill-effects due to the increasing consumption of fuel?
Ans. Harmful effects of using more fuels:
(i) Carbon fuels like wood, coal and petroleum release unburnt carbon particles. These fine particles create respiratory disorders and diseases like asthma.
(ii) Incomplete combustion of these fuels gives carbon monoxide. It is very harmful gas and causes respiratory disorders. It can kill persons sleeping in that room.
(iii) Excessive use of fuels causes global warming.
(iv) They cause acid rain which is harmful for crops, buildings and soil.