Class 8 Science Lesson 6 Inside Question and Answer NCERT & CBSE Board Here in this post. NCERT Class 8 Science Textbook Lesson 6 Inside Questions.
- Grade: VIII
- Lesson 6 Combustion and Flame.
Que. 1) fill in the blanks.
(1) The substance burn in air are called——-
(2) In flamble substances have very—– ignition temperature.
(3) —— is used to control fire.
(4) Fuels differ in their ——- and ——
Ans- efficiency and cost.
(5) Increases percentage of carbon dioxide in air has been linked to ———-
Ans- Global warming.
Que. 2) Answer the following questions.
Define the followings-
- Combustion- It is a chemical process in a substance reacts with oxygen to give off heat is called combustion.
- Ignition temperature- The lowest temperature at which a substance catches fire is called its Ignition temperature.
- Calorific value- The amount of heat energy produced on complete combustion of 1kg of a fuel is called calorific value.
- Acid rain- when oxides of sulphur and nitrogen dissolve in rain water and form acids and this rain is known as acids rain.
- Fuel – The sources of heat energy like charcoal , petrol, kerosene etc are called fuels.
(1) What is combustion?
Ans-It is a chemical process in which a substance reacts with oxygen to produce heat is called combustion. For the combustion air is necessary. There are Some substances undergoes combustion like petrol, kerosene, are known as fuel.
(2) How many types of combustion?
Ans- There are two types of combustion –Rapid combustion and Spontaneous combustion.
a) Rapid combustion- If gas burns rapidly and produces heat and light then this type of combustion is known as Rapid combustion.
b) Spontaneous combustion- If a combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion.
(3) What is fuel? Explain.
Ans-The sources of heat energy for domestic and industrial purpose like wood, charcoal, petrol, kerosene etc. are known as fuel. A food fuel is one in which is rapidily available. It is cheap. It burns easily in air at a normal rate. It produces a large amount of heat . It does not leave behind any undesirable substances. fuels are different in coast. Some fuels are cheaper than others.
(4) Give any few calorific values of fuels.
|Cow dung cake||
(5) What is global warming?
Ans-Global warming is the rise in temperature of the atmosphere of the earth. This results , among other things, in the melting of polar glaciers, which leads to a rise in the sea level ,causing floods in the coastal areas. Low lying coastal areas may even be permanently submerged under water. All this is known as Global warming.
(6) Give unit of calorific value.
Ans- The unit of calorific value is called Kilojoule per Kg ( Kj/Kg)
(7) Write short note on acid rain.
Ans-At the time of rainy seasons some time oxides of sulphur and nitrogen dissolve in rain water and form acids, such rain is called acid rain. It is very harmful for crops, buildings and soil. It is harmful for everything because it contains acids.
(8) Write short note on fire extinguisher.
Ans- Fire extinguisher is a device which is used to control fire. The most common fire extinguisher is water. But as we know water is used only when things like wood and paper are on fire. If electrical equipments is on fire we can not use water because it carries fire. So for this fires involving electrical equipments and inflammable materials like petrol, CO2 is the best extinguisher. CO2 beings havier than oxygen covers the fire like a blanket. Therefore the contact between the fuel and oxygen is cut off, the fire is controlled. The added advantage of CO2 is that in most cases it is not harmful the electrical equipment. This fire extinguisher we can see in every where like offices, school bus, buildings, stores etc and it is very useful.
(9) Define inflammable substance with examples.
Ans-The substance which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances. For example- petrol ,alcohol, LPG, etc.