Class 8 > Science


Give reasons. (a) Water is not used to control fires involving electrical equipment. (b) LPG is a better domestic fuel than wood. (c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.


(a)Water is only utilised when materials such as wood and paper are on fire as water may conduct electricity and hurt individuals attempting to extinguish a fire if electrical equipment is on fire. (b) LPG consists of volatile hydrocarbons such as propane and butane while wood is made up of complex biological hydrocarbons such as cellulose, hemicellulose and lignin. Combustion of LPG gives only carbon dioxide and water vapour while combustion of wood gives carbon dioxide, water vapour and ash, which is harmful when inhaled by people cooking the food causing them respiratory problems such as asthma. (c) The heat supplied to the paper cup is transferred to the aluminium pipe by conduction. So, in the presence of aluminium pipe, the ignition temperature of paper is not reached. Hence, it does not burn.

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