Class 8 Science Lesson 13 Inside Question

Class 8 Science Lesson 13 Inside Question and Answer NCERT & CBSE Board Here in this post. NCERT Class 8 Science Textbook Lesson 13 Inside Questions.

  • Grade: VIII
  • Lesson 13 Sound

Que. 1) fill in the blanks.

(1) The sound cannot travel through a —-

Ans- vaccum

(2) The vocal cords in men are about—-long.

Ans- 20mm

(3) Sound needs a medium for it’s ——

Ans- propagation.

(4) Frequency is expressed in —-

Ans-  Hertz.

(5) —- and — are two importance of a sound.

Ans- amplitude and frequency

(6) The frequency determines the ——- or —— of a sound.

Ans- shrillness or pitch

Que. 2) Define the followings.

(i) Vibration – the to and fro or back and forth motion of an object is called vibration.

(ii) Larynx- the sound producing organ in human is called larynx.

(iii) Eardrum-the sound enters in ear it travels  down a canal at the end of which there is  a thin stretched member it is called eardrum.

(iv) Oscillatory motion- the to and fro motion of an object is known as oscillatory motion and it is also known as vibration.

(v) Frequency-the number of oscillations per second is called the frequency.

Que. 3) answers the following.

(1) Give any two examples of musical instruments.

Ans- flute, table, harmonium etc.

(2) What happened when we pluck the string of sitar?

Ans- when we pluck the string of sitar the sound is produce. The sound is we hear  is not only that of the string the whole instruments is forced to vibrate and it is the sound of the vibration of the instruments that we hear. This is happened when we pluck the string of sitar.

(3) How sound produced in human beings?

Ans- when the lungs force air through the slit, the vocal cords vibrate , producing sound. Muscles attached to the vocal cords can make the cords tight or lose. When the vocal cords are tight and thin the type and quality of voice is different. So this is the procedures of sound producing in human being.

(4) Why the voices of men ,women and children are different?

Ans- the voice is depend on the vocal cords. Vocal cords produced the different type or quality of voice. The vocal cords in men are about 20 mm long . In women these are about 15 mm long. Children have very  short vocal cords. That is the reason of the different voice of men ,women and children.

(5) What is vaccum?

Ans-the vessel where absence of air then it is known as vaccum vessel. The absence of air is called vaccum. In this vaccum medium sound cannot travel.

(6) What is oscillatory  motion and frequency?

Ans- the to and fro motion of an object is known as vibration and this motion is called oscillatory motion The number of oscillations per second is called the frequency of oscillation. The frequency is expressed in hertz. Its symbol is Hz.

(7) How loudness of sound is depend on it’s amplitude and frequency? Explain.

Ans-The loudness of sounds depends on its amplitude because  when the amplitude of vibration is large the sound produced is loud. When the amplitude is small the sound produced is feeble.

Similarly the frequency determines the pitch of sound, means if the frequency of vibration is lower then the sound has a lower pitch. If the frequency of sound is high then it produce high pitch  it is clear from the above explanation the loudness of sound is depend on its amplitude and frequency.

(8) Give the difference between noise and music




Unpleasant sounds are called noise.

The sounds come  form musical instruments are called music.
The sound which make pollution is known as noise. Eg  sound of students in classroom , sound of vehicles etc.

The sound which make feel happy ,  pleasing to ear is known as music. Eg the sound produced by sitar, harmonium etc.

(9) Explain the noise pollution and its harm.

Ans- presence of excessive or unwanted sounds in the environment is called noise pollution. Major causes of sound pollution are vehicles, explosions including brusting of crackers, machines, loudspeakers etc. because of all these noise pollution increases.

Harms of noise pollution- the presence of excessive noise in the surroundings may cause many health related problems .lack of sleep, hypertension, , anxiety and many more health disorders may be caused by noise pollution. A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

(10) How can the noise pollution be controlled in a residential area?


  1. All noise operations must be conducted away from nay residential area.
  2. Noise producing industries should be set up away from such area.
  3. Use automobiles horns should be minimized.
  4. TV and music systems should be rum at low volumes.
  5. Trees must be planted along the roads and around buildings to cut down the sounds       reaching the residents, thus reducing the harmful effects of noise pollution.
Updated: December 19, 2020 — 1:55 pm

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