DAV Class 8 Science Solution Chapter 12 Sound
DAV School Books Class 8 Science Solution Chapter 12 Sound all Question Answer. DAV Class 8 12th Chapter Sound full Chapter explanation by expert teacher.
DAV School Books Class 8 Science Solution Chapter 12 Sound
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.
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 Sound travels fastest in solids (3) True (4) True (5) True (6) False, regular and periodic vibrations produce musical sounds
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 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) 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.
3.) Through which state of matter does sound propagate with the-
(a) slowest speed?
Answer: Gas.
(b) fastest speed?
Answer: Solid.
4.) Define the following terms. Also, write their SI units.
(a) amplitude
Answer: The highest value of a waveform or oscillation is its amplitude. metres is its SI equivalent (m).
(b) time period
Answer:A vibrating body’s time period is how long it takes for one entire cycle of oscillation to occur. Seconds are the SI time measurement (s).
(c) frequency
Answer: A sound’s frequency is expressed in hertz and indicates how many times a sound wave repeats every second (Hz).
5.) Name the characteristic of a vibrating body which determines the (a) loudness (b) pitch of the sound produced by it.
Answer: (a) A vibrating object’s amplitude is a characteristic that determines the amount of the vibrations it produces.
Answer: (b) The characteristic that determines the the pitch of the sound a vibrating body makes is its frequency.
6.) The frequencies, of the male and female voices in human beings, are nearly 1 kHz and 1.5 kHz. Which of the two voices-
(a) is likely to be flatter?
Answer: Male.
(b) has a higher pitch?
Answer: Female.
7.) When is a given sound regarded as a ‘musical sound’ or ‘music?
Answer: In general, a sound is regarded as musical if it is attractive and has some form of structure or rhythm.
Answer the following questions.
1.) Explain briefly the mechanism of production of sound in human beings.
Answer: In humans, sound is created whenever the voice box pulse. Vocal cords vibrate when air from the lungs is forced through them, sending sound waves across the air. After the sound waves enter our ears, the inner ear detects them and converts them into electrical signals, which are then transmitted to the brain and recognised as sound.
2.) How does the mechanism of production of sounds in birds differ from that in human beings?
Answer: In humans, sound is created by the vocal cords vibrating. The air moving through and surrounding the vocal tract modulates this vibration, creating the sounds of speech. Air sacs close to the syrinx, an organ found close to the base of the trachea, vibrate in birds to create sound. The air moving through the syrinx modifies this vibration, resulting in the complex bird songs.
3.) Describe a simple experiment to show that sound cannot propagate through vacuum.
Answer: It is possible to execute a straightforward experiment utilising two sealed containers and a vacuum between them to demonstrate that sound cannot travel across a vacuum. A sound-transmitting substance, such as air, should first be placed in one container. With a vacuum in between, the second container should be maintained entirely apart from the first. Both a vacuum sealer and a vacuum pump can be used to accomplish this. A sound source and a microphone should be put in the first and second containers, respectively, once the experiment is set up. The microphone shouldn’t pick up when the signal is on. This is so that sound, a mechanical wave, may travel through a medium like air or water. The absence of a medium in the space in between the two containers prevents the sound wave from passing through it.
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.
Answer: The oscillations of the wings are called beats here.
n = 3000 oscillations per second.
Duration, t = 5 s
frequency of the wings’ vibrations, v = n / t
v = 3000/5 = 600 Hz or 600 Hertz.
The audible frequency range is 20 Hz to 20 000 Hz.
The frequency of 600 Hz falls within the aforementioned range, making it audible.
5.) Explain why we always hear the thunder a little after we see the flash of lightning.
An electrical discharge known as lightning moves along a path made up of ionised air molecules. We can see an instantaneous event known as a lightning flash. Thunder is the noise produced when air that has been burned by a lightning strike rapidly expands. Our ears receive this sound at the speed of sound, or roughly 340 metres per second, from the lightning strike. We hear the thundering a bit after we see the lightning flash because sound travels more slowly than light.
6.) (a) Define loudness’ and ‘pitch’.
Answer: Loudness: The strength or loudness of a sound.
Pitch: the sound’s frequency, which establishes its high or low pitch.
(b) State the effect on the-
(i) loudness of a sound when the amplitude of the vibrating body increases.
Answer: The loudness of a sound increases with the increase in the amplitude of the vibrating object.
(ii) pitch of a sound when the frequency of the vibrating body increases.
Answer: The pitch of a sound will increase if the frequency of the vibrating body increases.
7.) Why is noise pollution regarded as harmful for human beings?
Since it has a major impact on both physical and mental health, noise pollution is considered to be detrimental for humans. Permanent hearing loss, communication problems, sleep disturbances, stress, and weariness are all risks associated with prolonged exposure to loud noise, which also raises the risk of developing cardiovascular disease. Additionally, noise pollution can raise the danger of accidents by making it more challenging to hear warning signals.