Class 8 Science - Chapter Combustion and Flame NCERT Solutions | Name the unit in which the calorific val

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                        .

Explain how the use of CNG in automobiles has reduced pollution in our cities.

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.

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

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 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.

Explain why some fibres are called synthetic.

Explain the importance of reproduction in organisms.

Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.

Explain why plastic containers are favoured for storing food.

Fill in the blanks:

(a) The planet which is farthest from the Sun is ____________ .
(b) The planet which appears reddish in colour is ____________ .
(c) A group of stars that appear to form a pattern in the sky is known as a ____________ .
(d) A celestial body that revolves around a planet is known as __________.
(e) Shooting stars are actually not ____________.
(f) Asteroids are found between the orbits of _________ and _________ .

Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?

If wheat is sown in the kharif season, what would happen? Discuss.

Explain in what way noise pollution is harmful to humans.

Image formed by a plane mirror is
(a) virtual, behind the mirror and enlarged
(b) virtual, behind the mirror and of the same size as the object
(c) real at the surface of the mirror and enlarged
(d) real, behind the mirror and of the same size as the object.

Explain how soil gets affected by the continuous plantation of crops in a field.