Class 8 Science - Chapter Combustion and Flame NCERT Solutions | Explain how the use of CNG in automobile

Make a labelled diagram of a candle 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.

Compare LPG and wood as fuels.

Explain how CO₂ is able to control fires.

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                        .

Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

Which zone of a flame does a goldsmith use for melting gold and silver and why?

Name the unit in which the calorific value of a fuel is expressed.

Which of the following can be beaten into thin sheets?
  (a) Zinc     (b) Phosphorus     (c) Sulphur     (d) Oxygen

Fill in the blanks
(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.
(b) The passage of an electric current through a solution causes ______________ effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.
(d) The process of depositing a layer ofany desired metal on another material by means of electricity is called .

Give two examples each of situations in which you push or pull to change the state of motion of objects.

Fill in the blanks:
(a) Friction opposes the _____________ between the surfaces in contact with each other.
(b) Friction depends on the _____________ of surfaces.                                                                                                                                                                      (c) Friction produces __________.
(d) Sprinkling of powder on the carrom board ________ friction.
(e) Sliding friction is ___________ than the static friction.

Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has irregular shape. (T/F)

Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.

Fill in the blanks:
(a) A place where animals are protected in their natural habitat is called                  .
(b) Species found only in a particular area is known as                          .
(c) Migratory birds fly to far away places because of                     changes.

Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain.

What are the different ways in which water gets contaminated ?

Explain the importance of reproduction in organisms.

An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

Prepare a brief speech on global warming that you have to make in your class.

Fill in the blanks in the following statements:
(a) To draw water from a well we have to ——— at the rope.
(b) A charged body ———— an uncharged body towards it.
(c) To move a loaded trolley we have to ———— it.
(d) The north pole of a magnet ———— the north pole of another magnet.

Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards

Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’:

Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Explain why some fibres are called synthetic.

Mark (✓) the correct answer:

Rayon is different from synthetic fibres because
(a) it has a silk like appearance
(b) it is obtained from wood pulp
(c) its fibres can also be woven like those of natural fibres

Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Describe an activity to show that thermoplastic is a poor conductor of electricity.