Chapter Review:

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• When an object vibrates, it produces sound.

• When any sound reflects by striking on any medium, that sound heard us again and again. This is called eco sound.

• The audible range of human ears is 20 Hz to 20,000 Hz. 

• The S.I unit of frequency is Hz (Hertz).

• The S.I unit of wave length is meter.

• The to and fro or back and forth motion of an object is termed as vibration.

• In humans, the sound is produced by the voice box or the larynx.

• The vocal cords in men are about 20mm long. In women these are about 5mm shorter.

• When air has been removed completely from a vessel, it is said that there is vacuum in the vessel.

• When sound enters in it, it travels down a canal at the end of
  which a thin membrane is stretched tightly. It is called the eardrum.

• The to and fro motion of an object is known as vibration. This motion is also called oscillatory motion.

• The number of oscillations per second is called the frequency of oscillation.

• The loudness of sound depends on its amplitude. When the amplitude of vibration is large, the sound produced is loud. When the amplitude is small, the sound produced is feeble.

• The loudness is expressed in a unit called decibel (dB).

• Unpleasant sounds are called noise.

• Some animals can hear sounds of frequencies higher than 20,000 Hz.
  Dogs have this ability.

• Sound travels through a medium (gas, liquid or solid). It cannot travel in vacuum.

Exercise

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1. Choose the correct answer :

Sound can travel through

(a) gases only

(b) solids only

(c) liquids only

(d) solids, liquids and air

Answer:

(d) solids, liquids and air

(a) Baby girl

(b) Baby boy

(c) A man

(d) A woman

Answer:

(c) A man

3. In the following statements, tick T against those which are true, and F against those which are false:

(a) Sound cannot travel in vacuum. (T/F)

(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)

(c) If the amplitude of vibration is large, sound is feeble. (T/F)

(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)

(e) The lower the frequency of vibration, the higher is the pitch. (T/F)

(f) Unwanted or unpleasant sound is termed as music. (T/F)

(g) Noise pollution may cause partial hearing impairment. (T/F)

Answer:

(a) T  (b) F  (c) F  (d) T  (e) F  (f) F  (g) T.

4. 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.

Answer:

(a) Time period  (b) amplitude  (c) hertaz  (d) noise  (e) frequency.

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

6. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?

7. Identify the part which vibrates to produce sound in the following instruments:

(a) Dholak 

(b) Sitar

(c) Flute

Answer:

Instrument	Part which vibrates to produse sound
(a) Dholak	Strechted membrane
(b)Sitar	Strechted string
(c) Flute	Air column

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

Answer:

The unpleasant sound is called noise, wherease pleasant sound is called music. Noise can produce so many health hazard, whereas music brings about soothing affect.

Yes, music become noise when musical instrument produce high volume sound.

9. List sources of noise pollution in your surroundings.

Answer:

The sound of bus, truck, construction, T.V., radio and loudspeaker etc.

10. Explain in what way noise pollution is harmful to humans.

Answer:

(i) Lack of sleep, hypertention, anxiety etc are some of the problems that may be caused due to noise pollution

(ii) A person who is exposed to a loud sound continously, may get temporary or even permanent deafness.

11. 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.

Answer:

I would suggest my parents to buy the house which is three lanes away from the roadside. This would protect us from noise pollution which is maximum on the roadside.

12. Sketch larynx and explain its function in your own words.

 

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Additional Questions With Solutions

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Ques: What is sound?

Ans: When an object vibrates, it produces sound.

Ques: What is eco sound?

Ans: When any sound reflects by striking on any medium, that sound heard us again and again. This is called eco sound.

Ques: What is minimum audible range for human ears?

Ans: The audible range is 20 Hz to 20,000 Hz.  

Ques: What is minimum audible distance from sound source to barrier medium?

Ans: 17.2 m.

Ques: What is S.I unit of frequency?

Ans: Hz (Hertz).

Ques: What is S.I unit of wave length?

Ans: S.I unit of wave length is meter.

Ques: By what organ human produces sound?

Ans: Vocal cord. (Larynx)

Ques: How do we produce sound?

Ans: Two vocal cords, are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air When the lungs force air through the slit, the vocal cords vibrate, producing sound.

Ques: In which mediums sounds propagate?

Ans: Solid, liquid and gas.

Ques: In which medium sound does not propagate?

Ans: Vacuum.

Ques: What is eardrum?

Ans: The shape of the outer part of the ear is like a funnel. When sound enters in it, it travels down a canal at the end of which a thin membrane is stretched tightly. It is called the eardrum.

Ques: Write the function of eardrum.

Ans: The eardrum sends vibrations to the inner ear.

Ques: What is oscillatory motion?                                                                

Ans: The to and fro motion of an object is known as vibration. This motion is also called oscillatory motion.

Ques: What is frequency? Write is its S.I unit?

Ans: The number of oscillations or vibrations per second is called the frequency of oscillation. The frequency is expressed in hertz (Hz).

Ques: On which measure does loudness of sound depend?

Ans: On its amplitudes.

Ques: What are two important properties of sound?

Ans: Amplitude and frequency are two important properties of any sound.

 

Additiona Questions With Answers

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Ques: Write the name of two properties of sound on basis of which sounds can differentiate?

Ans: we differentiate sounds on the basis of their amplitudes and frequencies.

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

Ans: Unpleasant sounds are called noise. Ex - the sounds produced by horns of buses and trucks.

While, Musical sound is one which is pleasing to the ear. Sound produced by a harmonium is a musical sound. The string of a sitar also gives out a musical sound. Musical sound may be noise if it is too loud.

Ques: What is noise pollution?

Ans: Presence of excessive or unwanted sounds in the environment is called noise pollution.

Ex - sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc.

Ques: List sources of noise pollution in your surroundings.

Ans: sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc.