NCERT Solutions for Class 8th Science
Chapter 6. Combustion And Flame
Text Book Exercise
Q1. List conditions under which combustion can take place.
Answer : Conditions under which combustion can take place are as follows :
(i) Air (oxygen), (ii) the ignition temperature should reach soon, and (iii) a source of inflammable substance.
Q2. Fill in the blanks:
(a) Burning of wood and coal causes of ....... air.
(b) A liquid fuel, used in homes is ............
(c) Fuel must be heated to its before it starts burning............. ...........
(d) Fire produced by oil cannot be controlled by .............
Answer : (a) pollution, (b) LPG, (c) ignition temperature, (d) water.
Q3. Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer : The use of CNG in automobiles has reduced pollution in our cities because CNG does not produce any poisonous gas/es on buring. That is why pollution in our cities is reduced.
Q4. Compare LPG and wood as fuels.
Answer : LPG burns easily and produces move heat in comparison to wood. Besides, it is a clan fual i.e., it does not produce fume and ashes as wood do.
Q5. 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.
Answer : (a) Water is not used to control fire produced by electrical ecuipment because water is a conductor of electricity and may result in electrocution or electric shock.
(b) LPG is asubstance which is readily available. It is cheaper and burns easily in air at moderate rate. It produces a large amount of heat and does not leave behind any undesirable substance. In case of wood, it does not burn that easily and produces a large amount of smoke which is very harmful for human beings. That is why, wood is not a better fuel than LPG.
(c) Paper catches fire easily, but when it is wrapped around an aluminium pipe and heat is suppiled then in presence of aluminium pipe, the ignition temperature does not meet, because heat given to it is passed to aluminium pipewhich lowers the temperture of the paper wrapped around it. That is why paper does not catch fire.