Sound is a chapter in DAV Class 8 Science book. The chapter discusses the basic fundamental terminologies like frequency of sound, vibration, the pitch of sound etc.
Sound Question Answers DAV Class 8
A. Fill in the blanks
1. Birds have a ring of cartilage, called ___________ in their wind pipes.
2. The SI unit of loudness of sound, is ___________.
3. The pitch of a sound is determined by its ___________.
4. Sounds, of frequency more than 20 kHz, are known as ___________.
5. An irregular, irritating sound is referred to as a ___________.
Answer:
(1) syrinx
(2) decibel
(3) frequency
(4) ultrasonic
(5) noise.
Also Check: Friction Question Answers DAV Class 8 Science Ch 5
B. Write True or False for the following statements.
1. Human beings, as well as all animals, have a voice box for producing their characteristic sounds.
2. Of the three mediums, solids, liquids and gases, sound propagates fastest in liquids.
3. Sound cannot propagate through vacuum.
4. Light propagates, through vacuum, with a speed that is nearly a million times more than the speed of sound in air.
5. The frequency of a given sound determines its ‘shrillness’ or ‘flatness”.
6. Irregular non-periodic vibrations generally produce musical sounds.
Answer:
(1) True
(2) False
(3) True
(4) True
(5) True
(6) 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 1.5 kHz. 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 then say that this is so-
Answer: Because it has anyone, 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) Sound 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?
Answer: Vibration.
2. Name two musical instruments which produce sound through vibrating strings.
Answer: Guitar and Sitar produce sound through the vibration of their strings.
3. Through which state of matter does sound propagate with the-
(a) slowest speed?
Answer: Sound propagates with the slowest speed in a gaseous medium.
(b) fastest speed?
Answer: Sound travels the fastest in a solid medium.
4. Define the following terms. Also, write their SI units.
(a) Amplitude
Answer: It can be called the maximum displacement or movement of a vibrating body on either side from the mean or the equilibrium position is called amplitude. Its SI unit is metres.
b) Time Period
The time taken for a vibrating body to complete one full oscillation is the time period, T. The SI unit of time period is second.
c) Frequency
Frequency is the number of oscillations completed in a second. The SI unit of frequency is Hertz. Hz
5. Name the characteristic of a vibrating body which determines the
(a) loudness (b) pitch of the sound produced by it.
a) Amplitude determines the loudness of a vibrating body
b) Frequency determines the pitch of a sound produced by it.
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 sound will be flatter
(b) Female’s voice has a higher pitch
7. When Is a given sound regarded as a ‘musical sound’ or ‘music’?
Answer: A given sound is regarded as musical sound when fixed number of oscillations are there in a given time period. The sound should also be soothing to our ears.
E. Answer the following questions.
1. Explain briefly the mechanism of production of sound in human beings.
The human body has two vocal chords, the larynx help humans to produce sound through the vocal chords. The structure is organized in such a way that there is air gap or slit between the 2 vocal chords.
The lungs pushes air towards the slit. This causes vibration between the 2 vocal chords and sound is produced.
2. How does the mechanism of production of sounds in birds differ from that in human beings?
Birds have a ring of cartilage (syrinx) instead of a larynx like humans. This is present in the windpipe. This helps them to produce different sounds. Humans have vocal chords and produce sound from them.
3. Describe a simple experiment to show that sound cannot propagate through vacuum.
Take a small bell jar. Fit a rubber cork inside it. Use a rod to pull a bell inside the rubber cork. Let the upper end of the rod be extended outside. Now shake the jar, you will notice that you can hear the sound of the vibration of the bell. This is because there is air inside the jar.
Now take a vacuum pump and evacuate all the air from the bell jar. Now shake the bell jar and try to listen to the voice. You will not be able to do so because there is absence of air.
4. 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 vibrations: 3000
time: 5 seconds
Frequency = Number of vibrations/ time
3000/5
= 600
5. Explain why we always hear the thunder a little after we see the flash of lightning.
Ans. We always hear the thunder a little later because the speed of light is much higher than the speed of sound
Speed of light: 3 x 10 power 8 m/s
Speed of sound: 330 m/s
Light has higher speed so we are able to see the flash of light in no time whereas the sound takes some seconds to reach our ears.
Loudness is the intensity of the sound, how much energy do the sound waves possess. The intensity is measured in decibels (dB).
Pitch: Sensation of the frequency is called as the pitch of the sound. High pitch means high frequency and low pitch means lower frequency.
7. Why is noise pollution regarded as harmful for human beings?
Noise pollution can affect the hearing capability of your ears. Noise has a direct impact on your eardrums. Continuous exposure to noise can cause serious damage to your ears.
Noise can also cause a lack of concentration. Noise can also cause irritation in some people.
So, these were Sound Question Answers of DAV Class 8 Science book. If you have any other queries, feel free to ask me through the comments section below Stay tuned to Careeradvice4u.
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