Class 8 Science - Chapter Light NCERT Solutions | State the laws of reflection.

Describe the construction of a kaleidoscope.

Draw a labeled sketch of the human eye.

Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table (b) Chalk powder
(c) Cardboard surface        (d) Marble floor with water spread over it
(e) Mirror                            (f) Piece of paper

How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?

(a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.21).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?

Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.

What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

Explain how you can take care of your eyes.

Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teachers advise?

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.

List conditions under which combustion can take place.

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.

What are the different ways in which water gets contaminated ?

Explain the importance of reproduction in organisms.

What happens when
(a) Dilute sulphuric acid is poured on a copper plate?
(b) Iron nails are placed in copper sulphate solution?
      Write word equations of the reactions involved.

Write short notes on the following:
(a) Cytoplasm
(b) Nucleus of a cell

Tick True/False against the following statements :

(a) Fossil fuels can be made in the laboratory. (T/F)
(b) CNG is more polluting fuel than petrol. (T/F)
(c) Coke is almost pure form of carbon. (T/F)
(d) Coal tar is a mixture of various substances. (T/F)
(e) Kerosene is not a fossil fuel. (T/F)

Describe characteristics and uses of coke.

What are the advantages of using CNG and LPG as fuels?

Fill in the blanks :
(a) Fossil fuels are               ,              and                       .
(b) Process of separation of different constituents from petroleum is called                 .
(c) Least polluting fuel for vehicle is                       .

Describe how coal is formed from dead vegetation. What is this process called?

Explain why fossil fuels are exhaustible natural resources.

Explain why chloroplasts are found only in plant cells?

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?