Explain various harmful effects of burning fuels.


Fuels are very useful for us. But there are certain disadvantages of burning fuels.

(i) Fuels like wood, coal, petroleum, etc. which are carbon fuels generally release unburnt carbon particles which are quite harmful. They cause various respiratory and skin diseases.

(ii) In most of the cases carbon dioxide is released during burning of fuels. This carbon dioxide is released in environment. This carbon increases the  temperature of the earth, which is called global warming.

(iii) Incomplete combustion of fuels release many poisonous gases like carbon monoxide in the environment. These poisonous gases create air pollution, such air if inhaled can be fatal.

(iv) Combustion of coal and diesel generates sulphur dioxide. It is a corrosive gas and it causes suffocation.

(v) Burning of petrol releases nitrogen oxides. These oxides of nitrogen and sulphur dioxide combine with rain water to cause acid rain. it affect aquatic life and natural environment.

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Explain why, fire caused by electricity should not be extinguished by pouring water.


Ordinary water conducts electricity to some extent. So, when water is thrown over the burning electrical appliance or burning electric wires, it can give electric shock to the person involved in fire-fighting. Thus, water should not be used to extinguish fires caused by electricity. 

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What are different types of combustion?


Combustion is of three types :

(i) Rapid combustion : When gases burn rapidly to produce heat and light it is called rapid combustion.

(ii) Spontaneous combustion : When any material like phosphorus burns on its own without any apparent cause, it is called spontaneous combustion.

(iii) Explosion : When combustion takes place with sudden release of heat and light and a large amount of gas in form of bang, it is called explosion as in case of crackers and bombs.

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Draw a diagram to explain that air is essential for combustion.



This diagram shows air is essential for combustion by analysing follo

This diagram shows air is essential for combustion by analysing following points:

a) The candle burns freely due to presence of air.

(b) The flame flickers and produces smoke because there is no air in case.

(c) In case flame finally goes off because air is not available.




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Describe how green house effect may cause atmospheric heating ? Name any two atmospheric constituents responsible for it.


Carbon dioxide molecules have the ability to absorb infra red radiations reflected from the earth. This trapping of infra red rays by the carbon dioxide molecules increases the temperature of the atmosphere. This is also known as green house effect.

Two gases that are responsible for causing green house effect are :

(i) Carbon dioxide

(ii) Methane

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