Class 8 Science - Chapter Sound NCERT Solutions | Which of the following voices is likely

Sketch larynx and explain its function in your own words.

Explain in what way noise pollution is harmful to humans.

List sources of noise pollution in your surroundings.

Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.

Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain?

Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called ................... .
(b) Loudness is determined by the .........................of vibration.
(c) The unit of frequency is..........................
(d) Unwanted sound is called ......................... .
(e) Shrillness of a sound is determined by the ................. of vibration.

Identify the part which vibrates to produce sound in the following instruments:
(a) Dholak (b) Sitar (c) Flute

A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

What is the difference between noise and music? Can music become noise sometimes?

Choose the correct answer :
Sound can travel through
(a) gases only (b) solids only
(c) liquids only (d) solids, liquids and gases.

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.

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 ?

Fill in the blanks in the following :
(a) A person 1 m in front of a plane mirror seems to be _______________ m from his image.
(b) If you touch your ____________ ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with ____________
(c) The size of the pupil becomes ____________ when you see in dim light.
(d) Night birds have ____________ cones than rods in their eyes..

What is irrigation? Describe two methods of irrigation which conserve water.

Choose the most appropriate answer:
(a) Internal fertilization occurs
      (i) in the female body.
      (ii) outside the female body.
      (iii) in male body.
      (iv) outside male body.

(b) A tadpole develops into an adult frog by the process of
      (i) fertilization   (ii) metamorphosis   (iii) embedding    (iv) budding

(c) The number of nuclei present in a zygote is
      (i) none   (ii) one    (iii) two    (iv) four

What is the term used for secretions of endocrine glands responsible for changes taking place in the body?

Give examples to show that friction is both a friend and a foe.

Complete the crossword with the help of clues given below:
Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.

Down
1. Green plastids.
2. Formed by collection of tissues.
4. It separates the contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.

Answer in brief:
(a) Why should we conserve biodiversity?
(b) Protected forests are also not completely safe for wild animals. Why?
(c) Some tribals depend on the jungle. How?
(d) What are the causes and consequences of deforestation?
(e) What is Red Data Book?
(f) What do you understand by the term migration?

Explain briefly the life cycle of a frog.

Match items in column A with those in column B.
               A                                       B
  (i) Kharif crops                    (a) Food for cattle
  (ii) Rabi crops                     (b) Urea and super phosphate
  (iii) Chemical fertilisers       (c) Animal excreta, cow dung urine and plant waste
  (iv) Organic manure           (d) Wheat, gram, pea
                                             (e) Paddy and maize

Give reasons for the following:
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.