Students can download Class 8 Science Chapter 14 World of Sounds Important Questions, KSEEB Class 8 Science Important Questions and Answers helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.
Karnataka State Syllabus Class 8 Science Important Questions Chapter 14 World of Sounds
Question 1.
What is sound?
Answer:
Sound is a form of energy. It is a physical sensation sensed by our ears.
Question 2.
List some sources of sound.
Answer:
Sound can come from many sources. It includes people, machines, animals, motor vehicles, horns, loudspeakers, construction and transport systems, aircraft movements, sirens, music systems, radio and fireworks.
Question 3.
Demonstrate a simple activity to show that sound can do work.
Answer:
Sound can be said to be a form of energy if it can do work. Take a thin strip of paper. Hold it near a loud speaker. The paper strip flutters showing that sound can do work. This establishes that sound is a form of energy.
Question 4.
Can sound be converted into other forms of energy? Give an example.
Answer:
Yes, sound can be converted into other forms of energy. For example, sound is converted into electrical energy in a microphone.
Question 5.
What are the various functions of sound?
Answer:
Sound is a means of communication. It can be a signal of alarm or danger. It may be a way of drawing attention. Sound could be an expression of one’s ideas and emotions. Sound could be a means of entertainment.
Question 6.
How is sound produced?
Answer:
Sound is produced by the vibration of objects or materials.
Question 7.
What is the condition required for the propagation of sound?
Answer:
Material medium is necessary for the propagation of sound.
Question 8.
Describe a simple activity to show that we produce sound by vibrations.
Answer:
Sit comfortably in a chair. Place one of your hands firmly midway on the throat. Say ‘ahhhhhh ….’ as long as you can. Feel the vibrations at the fingertips. On stopping the sound, the vibrations also stop. This show s that we produce sound by vibrations.
Question 9.
Describe an activity to show that sound is produced by the vibration of bodies.
Answer:
Stretch a rubber string tightly between two supports. Pluck the string. The strung begins to vibrate producing a sound. Stop the vibrations. The sound also stops. This shows that sound is produced by the vibrations of bodies.
Question 10.
How do the following musical instruments produce sound: Guitar, Mridangiim, violin, flute and harmonium?
Answer:
Guitar and violin produce sound by the vibration of strings. Mridangam produces sound by the vibration of a membrane. Flute produces sound by the vibration of the air column. Harmonium produces sound by the vibration of reeds.
Question 11.
Describe an activity to show that sudden expansion of gases produces sound.
Answer:
Take a balloon. Start blowing air into it from the mouth. The balloon grows in size. Continue to blow air till the balloon bursts. Suddenly we hear a loud sound. This sound is caused by sudden expansion of air.
Question 12.
Give a natural situation where sudden expansion of air produces a loud sound.
Answer:
When lightning occurs, there is sudden expansion of air. This produces a loud sound which is heard as thunder.
Question 13.
Explain the mechanism of production of sound in human beings.
Answer:
When we speak or sing, we produce sound with the help of a special structure called ‘voice box’. It is also called larynx. This is located at the upper end of the windpipe (trachea). The larynx contains two membranes called vocal cords. They stretch across the voice box.
The stretching leaves a small gap between the membranes to form a small slit. When we wish to produce sound, we push air through the slit which causes the vocal cords to vibrate. The vibrations of the vocal cords produce sound.
Question 14.
Make a list of five musical instruments. State how each of them produces sound.
Answer:
| Musical instrument | The way it produces sound |
| Veena | Vibration of a stretched string |
| Sitar | Vibration of a stretched string |
| Tabla | Vibration of a stretched membrane |
| Drum | Vibration of a stretched membrane |
| Trumpet | Vibration of air column |
| Saxophone | Vibration of air column |
Question 15.
How does sound reach our ears from a source?
Answer:
Sound is a form of energy. The energy produced by a vibrating body travels through the medium in the form of waves. These waves cause a disturbance in the medium. The disturbance travels through the medium carrying energy. The disturbance occurs in the form of contractions and rarefactions.
Question 16.
Explain the mechanism of transmission of sound through air.
Answer:
Imagine that you are listening to a sound from a source. The source transmits energy to the surrounding medium namely air. The energy makes the air particles to compress. The compressed particles transmit their energy to the next neighbouring particles.
Thus there will be a scries of compressions and rarefactions in air before the sound reaches the ears. The vibrations of the particles of air occur back and forth in the direction of sound itself.
Question 17.
Describe an experiment to show that sound requires a material medium for its,propagation.
OR
Describe an experiment to show that sound cannot travel in vacuum.
Answer:
Take a bell jar and place it over a vacuum pump. Suspend a mobile phone inside the bell jar as shown in the figure. Make the apparatus airtight. When you call the mobile, the ringtone is heard. Now use the vacuum pump and remove the air from the bell jar gradually.
The ringtone becomes increasingly feeble. After sometime, the ringtone is not heard although the phone is seen ringing. This shows that sound requires a material medium for its propagation.
Question 18.
Describe an activity to show that sound is produced by vibration of materials.
Answer:
A long metal strip is held firmly on to a table. Its free end is pulled down and let go. When the free end is vibrating we can hear the sound. When we hold the vibrating strip with our hand the vibrations stop and there is no sound.
Question 19.
Describe an activity to show that solids conduct sound much better than air.
OR
Describe an activity to show that sound can travel through solids.
Answer:
Place one of your ears firmly on a wooden table. Ask a friend to scratch the table at the other end. You hear the sound of scratching loudly and clearly. Now lift your head from the table and ask your friend to scratch the table again. You do not hear the sound clearly or loudly. This shows that solids conduct sound much better than air.
Question 20.
Represent a wave graphically. Show in the diagram, the wavelength and amplitude.
Answer:
Question 21.
How do you describe a sound wave?
Answer:
A sound wave is generally described in terms of its wavelength, frequency, amplitude and speed.
Question 22.
Give the meaning of the following terms with reference to a sound wave
- Wavelength
- Frequency
- Amplitude
- Speed.
Answer:
1. Wavelength:
Sound is a longitudinal wave. This means the particles of the medium through which sound travels will show a series of compressions and rarefactions. When a sound wave travels through a medium, the distance between two successive .com press ions is called the wavelength of the sound wave. It is the same as the distance between two rarefactions. Wavelength is usually represented by the symbol X (lambda).
2. Frequency:
The number of times an object vibrates in 1 second is called frequency. The frequency of a sound wave is same as the frequency of the source.
3. Amplitude:
When sound travels through a medium, the highest displacement of a particle from its rest position is called the amplitude of sound.
4. Speed:
The distance travelled by sound in 1 second is called its speed.
Question 23.
What is the S.I. unit of the following: wavelength, frequency, amplitude and speed?
Answer:
The S.I. unit of wavelength is ‘metre’. The S.I. unit of frequency is called ‘hertz’ (Hz). The S.I. unit of amplitude is ‘metre’ and the S.I. unit of speed is ‘metre per second’ (m s-1)
Question 24.
What is the relationship between velocity, frequency and wavelength of a sound wave?
Answer:
The velocity of sound is equal to the product of its frequency and wavelength.
Question 25.
What aspect of a sound wave is determined by its ‘frequency’ and ‘amplitude’?
Answer:
The pilch (shrillness) of sound is determined by its frequency. Higher the frequency of sound higher would be its pitch. The loudness of sound is determined by its amplitude. Higher the amplitude, higher would be its loudness.
Question 26.
What is the speed of sound in air?
Answer:
The speed of sound through air at sea level is about 346 m s-1
Question 27.
What is sonic boom?
Answer:
When an object such as an aircraft travels faster than sound, an impulsive noise is suddenly produced. This is known as sonic boom.
Question 28.
Why is sound considered a longitudinal wave?
Answer:
The particles of the medium through which sound travels vibrate in the direction of sound back and forth. This is why sound is considered a longitudinal wave.
Question 29.
What is the unit used to express the volume or intensity of sound?
Answer:
The volume or intensity of sound is measured in decibel (dB).
Question 30.
Define the frequency of a sound wave. If 40 wavelengths of a sound wave travel through a point in 5 second, what is the frequency of the wave?
Answer:
The number of times an object vibrates in one second is called frequency.
Number of wavelengths passing through a point = 40
Time taken = 5 s
Frequency = ?
Question 31.
What is reflection of sound?
Answer:
When sound hits an obstacle, a part of its energy is turned back. This phenomenon of bouncing back of sound from an obstacle is called reflection of sound.
Question 32.
List two applications of reflection of sound.
Answer:
Reflection of sound causes echo effect. It also finds applications in medicine and entertainment. The whispering gallery in Gol Gumbaz in Bijapur is also based on reflection of sound.
Question 33.
What is echo? How does it occur?
Answer:
Repeated hearing of the same sound due to reflection of sound waves from a surface is called echo. Echo is the direct result of reflection of sound.
Question 34.
Why don’t we hear an echo in small rooms?
Answer:
There must be certain minimum distance between the observer and the obstacle to hear an echo clearly. Since that distance is smaller in small rooms, echo is not heard. .
Question 35.
What should be the minimum distance between a person shouting and the reflecting surface to hear the echo?
Answer:
The sensation of sound persists in our brain for about 0.1s. To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s. If we take the speed of sound to be 346 m/s the sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1 s.
Hence, the total distance covered by the sound from the point of generation to the reflecting surface and back should be atleast (346 m/s) 0.1 s = 34.6 m. Thus, for hearing distinct echoes, the minimum distance of the reflecting surface from the source of sound must be half of this distance, that is, 17.3 m or approximately 17 m.
Question 36.
Describe an experiment to show that reflection of sound occurs according to certain laws.
Answer:
Take two identical long pipes. Arrange them on a table near a wall as shown in the figure. Keep a clock near the open end of one of the pipes. Try and hear the sound of the clock through the other pipe by placing your ear close to it. Adjust the position of the pipes so that you can best hear the sound of the clock.
Now, measure the angles of incidence and reflection. It is found that the two angles would be equal. Lift the pipe on the right vertically to a small height and observe what happens. The sound is either not heard or heard feebly. This shows that the incident sound and the reflected sound will be in the same plane.
Question 37.
Why do we hear echo clearly in an empty big hall and not so clearly when the hall is furnished with furniture, window curtains?
Answer:
The various materials such as window curtains and furniture absorb some amount of sound and hence the echo is not heard clearly in big halls equipped with lot of material.
Question 38.
What is noise pollution?
Answer:
Excessive displeasing and unwanted sound that disrupts the activities of human or animal life is called sound pollution or noise pollution.
Question 39.
List some common sources of noise pollution.
Answer:
Noise pollution can occur because of transport, industries, people, loudspeakers, factories, horns of vehicles, machines, etc.
Question 40.
Mention some of the ill-effects of noise pollution.
Answer:
Noise pollution may cause such effects as irritation, headache, loss of concentration, increased blood pressure, enlargement of pupils and palpitation of the heart. Loud sounds may damage the eardrum and even result in partial or complete loss of hearing.
Multiple Choice Questions
Question 1.
Imagine that you are listening to a popular song on a radio. When you increase the volume slightly, the factor related to sound wave which is increased during the process is
(a) frequency
(b) Wavelength
(c) amplitude
(d) both frequency and wavelength
Answer:
(c) amplitude
Question 2.
Sound waves cannot travel through
(a) solids
(b) liquids
(c) gases
(d) vaccum
Answer:
(d) vaccum
Question 3.
The factor that is transmitted in wave motion is
(a) particles of the medium
(b) vibration of the particles
(c) energy of the source
(d) electrons in the medium
Answer:
(c) energy of the source
Question 4.
The velocity of sound is highest in
(a) air
(b) glass
(c) water
(d) vaccum
Answer:
(b) glass
Question 5.
Sound waves are
(a) longitudinal
(b) transverse
(c) partly longitudinal and partly transverse
(d) sometimes longitudinal and sometimes transverse
Answer:
(a) longitudinal
Question 6.
The unit of quantity on which pitch of the sound depends is
(a) metre
(b) hertz
(c) metre/second
(d) second
Answer:
(b) hertz
Question 7.
In an unoccupied hall of a choultry, you will experience an echo. If the same hall is furnished with almirahs, tables, chairs and other materials you will not experience echo clearly. This is because
(a) sound waves get absorbed by the objects in the hall
(b) the area of reflecting surface will decrease
(c) reflected sound is reflected again
(d) sound does not get reflected.
Answer:
(a) sound waves get absorbed by the objects in the hall
Question 8.
In musical octaves ‘sa’, ‘re’, ‘ga’, ‘ma’, ‘pa’, ‘da’, ‘ni’, ‘sa’, the first ‘sa’ differs from the last ‘sa’ regarding
(a) wavelength
(b) amplitude
(c) frequency
(d) velocity
Answer:
(c) frequency
Question 9.
Sound waves belong to this category
(a) electromagnetic
(b) transverse
(c) longitudinal
(d) circular
Answer:
(c) longitudinal
Question 10.
Sound waves are produced by
(a) vibrations
(b) magnetic field
(c) electric field
(d) air
Answer:
(a) vibrations
Question 11.
The velocity of sound in medium is 330 m s-1. If the wavelength of the sound is 0.1 m, the frequency
(a) 33 Hz
(b) 3300 Hz
(c) 3.3 Hz
(d) 660 Hz
Answer:
(b) 3300 Hz
Question 12.
In Golgumbaz, if you make a sound it will be heard seven times. It is due to
(a) refraction of sound
(b) seven flat surfaces in the gumbaz
(c) reflection of sound
(d) short distance between the gumbaz and the source of sound
Answer:
(c) reflection of sound
Question 13.
In Ladakh region, the conversation between two soldiers at a distance of 100 m between them will not be clear. It is mainly due to
(a) adsorption of sound by the trees
(b) absorption of sound by the trees
(c) at a high altitude the air density will be low
(d) at a high altitude there is low temperature
Answer:
(c) at a high altitude the air density will be low
Fill In The Blanks
(1) The product of frequency and wavelength of a sound wave gives its velocity
(2) The S.I. unit of wavelength of sound is metre
(3) The velocity of sound in air is about 346 m s-1
(4) Sound cannot travel through vacuum
(5) Echo is caused by of sound reflection
(6) The distance between two successive compressions of a longitudinal wave is called its wavelength
(7) The height of a wave is called its amplitude
(8) A periodic disturbance travelling through a medium carrying energy is called wave
(9) The number of times on object vibrates in one second is called frequency
(10) is a device that increases the amplitude of a wave Amplifier
(11) The distance travelled by sound in one second is called its speed