Chapter 12 | Sound | Class- 8 DAV Science Solutions

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Topics and Sub Topics in Class 8 Science Chapter 12 Sound

Production of Sound
Propagation of Sound
Reflection of Sound
Range of Hearing
Applications of Ultrasound
Structure of Human Ear

DAV Class- 8 Science Sound Question and Answer

Something To Know

A. Fill in the blanks.

1. Birds have a ring of of cartilage, called syrinx in their windpipe.

2. The SI unit of ‘loudness’ of sound, is bel.

3 The pitch of a sound is determined by its frequency.

4. Sounds, of frequency more than 20kHz, are known as ultrasonic.

5. An irregular, irritating sound is referred to as a noise.

B. State True or False for the following statements.

1. Human brings, as well as all animals, have a voice box for producing their characteristic sounds.	True
2. Of the three mediums, solids, liquid and gases, sound propagates fastest in liquids.	False
3. Sound cannot propagate through vacuum.	True
4. Light propagates, through vacuum, with a speed that is nearly a million times more than the speed of sound in air.	True
5. The frequency of a given sound determines its ‘shrillness’ or ‘flatness’.	True
6. Irregular non-periodic vibrations generally produce musical sounds.	False

C. Tick (✓) the correct option.

1. The maximum displacement of a vibrating body, on either side of its mean position, is known as its –

Answer: Amplitude

2. The frequency of a given sound is 1.5hz. The vibrating body is then –

Answer: Completing 1,500 vibrations in one second.

3. Sound can propagate through –

Answer: All the three states of matter.

4. When lightning and thunder take place, they occur –

Answer: Together but the thunder is observed a little after the lighting.

5. A given sound is inaudible to the human ear. We can say that this is so –

Answer: Because it has any one, or more, of the three characteristics listed above.

6. The following are some statements about sound:

(i) Sound propagates faster in steel than in air.

(ii) Sounds are produced through vibrations.

(iii) Sounds propagates faster than light.

(iv) Sound does not require a medium for its propagation.

Out of these, the correct statements are –

Answer: (i) and (ii) only

D. Answer the following questions in brief.

1. Name the cause that is regarded as the basic cause of all sounds?

The basic cause of Sound is the vibration of particles. Vibrations of particles cause vibration in the medium in which the particles are present. The medium may be air, water, etc, which help in the propagation of the sound waves.

2. Name two musical instruments which produce sound through vibrating strings.

Guitar and sitar are two musical instruments with vibrating strings that make sound. The vibrating part in a sitar are stretched strings. Sound is produced due to the vibration of stretched string.

3. Through which state of matter does sound propagate with the—(a) slowest speed? (b) fastest speed?

Ans. (a) Gas, (b) Solid

4. Define the following terms. Also, write their SI units. (a) amplitude (b) time period (t) frequency

(a) The maximum distance from the mean position to which a vibrating body moves is called amplitude.

SI unit of amplitude is meter.

(b) Time taken to complete one oscillation is called time period.

The SI unit of time period is second.

The SI unit of frequency is hertz.

5. Name the characteristic of a vibrating body which determines the—
(a) loudness (b) pitch of the sound produced by it.

Ans. (a) Amplitude, (b) Frequency

6. The frequencies, of the male and female voices in human beings, are nearly I kHz and 1.5 kHz. Which of the two voices—(a) Is likely to be flatter? (b) has a higher pitch?

Ans. (a) Male, (b) Female 7. When is a given sound

7. When Is a given sound regarded as a ‘musical sound’ or ‘music’?

Ans. When the sound is pleasant it is called music. Musical sounds are produced by regular or periodic vibrations.

E. Answer the following questions.

I. Explain briefly the mechanism of production of sound in human beings.How does the mechanism of production of sounds in birds differ from that in human beings?

Ans: In birds the sound producing organ is syrnx and that of humans or we can say in mammals it’s the larynx which has vocal cords. The mechanism of producing sound in birds differ from that in human beings because birds have a ring of cartilage called syrinx in their windpipe they use it in their voice Box to produce sound but in human beings there is a vocal chords or larynx which help us to produce sound.

2. Describe a simple experiment to show that sound cannot propagate through vacuum.

Ans: Sound cannot travel through vacuum. This can be shown by the following experiment:
A ringing electric bell is placed inside an airtight bell jar containing air. We can hear the sound of the ringing bell clearly. Thus, when air is present as medium in the bell jar, sound can travel through it and reach our ears.

3.On a hot summer day, a little mosquito produces a warning sound near your ear by vibrating its wings at the rate of 3,000 wing beats per five seconds. State the frequency, in hertz, of this sound.

Ans: Number of oscilation:3000 , Time=5 sec

Frequency:Number of Oscilliation/Time

= 3000 / 5 sec =600 Hz

5. Explain why we always hear the thunder a little after we see the flash of lightning.

Ans. The speed of light is more than the speed of sound. Due to this, we always hear the thunder a little after we see the flash of lightning.

6. (a) Define *loudness’ and ‘pitch’. (b) State the effect on the—

(i) loudness of a sound when the amplitude of the vibrating body increases.

(ii) pitch of a sound when the frequency of the vibrating body increases.

Ans. The intensity of sound is called its loudness. Loudness increases with increase in amplitude. Pitch: The shrillness or flatness of sound is called its pitch. Pitch increase with increase in frequency.

7. Why is noise pollution regarded as harmful for human beings?

Ans.

Noise pollution affects both health and behavior. Unwanted sound (noise) can damage physiological health. Noise pollution can cause hypertension, high stress levels, tinnitus, hearing loss, sleep disturbances, and other harmful and disturbing effects.

Value-Based Questions

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