NCERT Question 5 - Chapter 6 Class 8 - Combustion And Flame

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

Give reasons.

1. Water is not used to control fires involving electrical equipment because

     Water is a good conductor of electricity. When water is thrown on an electrical equipment which is 

     on fire, water may conduct electricity and cause electric shock to the person who is trying to extinguish it

     B. LPG is a better domestic fuel than wood because

• • LPG burns without producing smoke, but burning of wood produces lot of smoke
  • LPG has a higher calorific value than wood, so 1 kg of LPG produces much more heat than wood
  • LPG is easier to transport in cylinders than wood
  • Burning of wood leaves behind ash,which can cause respiratory diseases like Asthma but LPG doesn’t leave behind any residue
    
    

     C. Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not because

           Aluminium is a good conductor of heat. 

           So in the presence of the aluminium pipe, heat gets transferred from paper to aluminum pipe. Since heat gets transferred,

           the ignition temperature of paper is not reached. Hence it does not catches fire easily