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Karnataka State Syllabus Class 8 Science Chapter 14 World of Sounds
KSEEB Class 8 Science World of Sounds Textbook Exercise Questions and Answers
I. Four alternatives are given to each of the following incomplete statements/questions. Choose the correct answer.
Question 1.
Imagine that you are listening to a popular song from a radio using volume control knob, you slightly increase the volume. The factor related to a sound wave in this process is the increase in
(a) frequency
(b) velocity
(c) amplitude
(d) both frequency and wave length
Answer:
(c) amplitude
Question 2.
The velocity of sound is highest in
(a) air
(b) water in Human beings.
(c) glass
(d) vacuum
Answer:
(c) glass
Question 3.
In an unoccupied hall of a choultry, you will experience the echo effect of sound. If the same hall is furnished with almirahs, tables, chairs, and other commodities, you will not experience the echo clearly. It is because
(a) sound waves get absorbed by the objects in the hall.
(b) the area of reflecting surface decreases.
(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 4.
The factor that is transmitted in wave motion is
(a) particles of the motion
(b) vibration of particles
(c) energy of the cause of the wave
(d) electrons of the medium
Answer:
(d) electrons of the medium
II. Fill in the blanks with suitable words:
Question:
1. The product of frequency and wavelength of a sound wave is equal to its _____________.
2. The SI unit of wavelength is _____________.
3. The velocity of sound in air at 25° C is approximately _____________.
Answer:
1. velocity,
2. Lambda,
3. 346 m/sec.
III. Answer the following:
Question 1.
Why is sound a longitudinal wave?
Answer:
Sound is a longitudinal wave because it is a mechanical wave in which the vibration of particles is parallel to the direction of the sound.
Question 2.
Explain an activity to show that sound can do work.
Answer:
Take a thin strip of paper. Hold it near the speaker cone of a loudspeaker and the paper starts moving. This shows that sound can do work.
Question 3.
Describe an activity to show that the sound is produced by the vibration of materials.
Answer:
Take a rubber string. Stretch it tightly between two supports. Pluck the string, the string begins to vibrate. Then we will be able to hear some sound. Stop the movement of the string. Even the sound also stops. From this activity, we can show that the sound is produced by the vibration of materials.
Question 4.
Make a list of five musical instruments. State how each of them produces sound.
Answer:
Musical Instrument.
The way Lt produces sound:
1. by the vibration of air 2. by the vibration of the membrane 3. by the vibration of air 4. by the vibration of string 5. by the vibration of the string
- Flute
- Tabla
- Harmonium
- Sitar
- Guitar
Question 5.
List two applications of reflection of sound.
Answer:
- eco-ranging. By using ultrasound signals sent by sonar to the sea bottom and knowing the velocity of sound in water the depth of the sea at a point can be calculated.
- Ultrasound Scanner is an invaluable diagnostic tool for examining fluid-filled organs such as bladders, kidneys, etc.
Question 6.
Describe an activity to that the sound requires a material medium for its propagation.
Answer:
A gets feebler and phone feebler and after a point can not be heard vacuum pump anymore. Suspend a mobile phone inside an airtight glass bell jar as shown in the diagram. Connect the bell to a vacuum pump. When a call is made to that phone, the ringing tone is heard. Start removing the air from the jar by Using the vacuum pump. The ringing tone gets feebler and feebler and after a point cannot be heard anymore. This experiment shows that sound cannot travel in a vacuum, as it needs a material medium for its propagation.
Question 7.
Represent a wave graphically. Show in the diagram, the wavelength, and amplitude.
Answer:
Think
Question 1.
Why is sound both a boon and a bone?
Answer:
A pleasant sound like Hello sir/Hello madam while addressing a person or hearing musical notes are boon and a loud sound may cause irritation, headache, and loss of concentration. Long exposure to such sounds may lead to loss of sleep, tension and stress, high blood pressure, heart trouble, etc. Therefore such sounds are bone to us.
Question 2.
What measures would you take to minimize the sound disturbance caused to others?
Answer:
The steps to be taken to minimize the sound disturbance are as follows
- Turn off your electronic systems. When not in use and also to not play them too loudly
- Soundproof your music playing areas.
- Plant more trees.
- Regular maintenance of vehicles and machines.
- Use earplugs.
KSEEB Class 8 Science World of Sounds Additional Questions and Answers
Question 1.
What is sound?
Answer:
A sound is a form of energy which excites in our ears the sensation of hearing.
Question 2.
What produces sound?
Answer:
Sound is produced by a vibrating body.
Question 3.
What are the waves?
Answer:
Energy moves through a medium by creating a disturbance in it. These disturbances may repeat themselves at regular intervals. Such periodic disturbances which constitute a pattern are called waves.
Question 4.
What are transverse waves?
Answer:
Transverse waves are the waves, on which the particles of the medium vibrate perpendicularly to the line of propagation, for example – water waves.
Question 5.
How do Dolphins and Whales live in water communicate?
Answer:
Dolphin and Whales produce and use different kinds of sounds and whistles. These sounds travel through water and pass on messages to others. Some species of dolphins send special sounds to identify themselves.
Question 6.
What is meant to be wavelength?
Answer:
The distance between two successive compressions is called wavelength of the sound wave. This is equal to the distance between two successive rarefactions. The wavelength is represented by Lamda ‘λ’
Question 7.
What is the frequency?
Answer:
The number of times an object vibrates in one lambda second is called frequency. The number of compressions that pass through a point in one second also gives frequency. S I unit of frequency is hertz., the symbol is Hz.
1 hertz (Hz) = 1 wave per second or cycle per second
Question 8.
What is meant by the amplitude of a sound wave?
Answer:
The highest displacement of a particle from its rest position is the amplitude of the sound.
Question 9.
What is the speed of sound?
Answer:
The speed of sound is the distance traveled by it in one second. S I unit of speed is metre per second is ms-1.
Question 10.
What do you mean by a sonic boom?
Answer:
When a plane travels faster than the speed of sound, the plane breaks the sound barrier and produces a loud sound. This is called a sonic boom.
Question 11.
What is meant by the Echo?
Answer:
The reflection of sound is called Echo.
Question 12.
Mention the harmful effects of noise pollution.
Answer:
A loud sound may cause irritation, headache, and loss of concentration. Long exposure to such sounds may lead to loss of sleep, tension and stress, high blood pressure, heart problems, and hearing loss. Noise causes many adverse effects on animals also. It is a disadvantage for birds that rely on hearing to locate prey.
II. Fill in the blanks:
1. Sound is a form of ___________________.
2. Any vibrating body produces ___________________.
3. The art of imitating other sounds is called ___________________.
4. Voice box of human beings is called ___________________.
5. The type of motion due to compression and rarefaction is ___________________.
6. Sound cannot travel in ___________________.
7. Different sounds have ___________________ Wave lengths.
8. Faster the vibration, ___________________ the frequency.
9. The product of frequency and wave length of a wave is the ___________________ of the wave.
10. Higher the amplitude, higher the ___________________ of the sound.
11. The device that increases the amplitude of a wave is ___________________.
12. The first person to fly a plane which produced sonic boom was ___________________.
13. The name of the plane which had a speed faster than the speed of sound is ___________________.
14. The speed of light is ___________________ than the speed of sound.
15. Rolling of thunder is due to the success ___________________ of the sound waves on the clouds
16. Unwanted sound is called as ___________________.
17. Pleasant sound is called as ___________________.
18. Excessive or unwanted sound leads to ___________________.
Answer:
1. energy,
2. sound,
3. Mimicry,
4. larynx,
5. longitudinal,
6. vacuum,
7. different,
8. higher,
9. velocity,
10. volume,
11. Amplifier,
12. Chuck Yeager,
13. X-1,
14. more,
15. reflections,
16. noise,
17. music,
18. noise pollution.
III. Choose the correct alternative.
Question 1.
The true statement among the following is:
(a) sound travels faster than light
(b) sound can travel through a vacuum.
(c) sound travels faster in a vacuum.
(d) sound requires a medium to propagate.
Answer:
(d) sound requires a medium to propagate.
Question 2.
In humans, the sound is produced by the vibration of
(a) Larynx
(b) Vocal cords
(c) Tongue
(d) Palate
Answer:
(b) Vocal cords
Question 3.
The loudness of a sound is measured in
(a) joule
(b) kilowatt
(c) Decibel
(d) phone
Answer:
(c) Decibel
Question 4.
The loudness of the sound is determined by its
(a) amplitude
(b) frequency
(c) speed
(d) pitch
Answer:
(a) amplitude
Question 5.
We see lightning first and hear the sound of thunder a little later because
(a) lightning occurs first and then thunder
(b) Thunder occurs at a greater height
(c) Light travels much faster than sound.
(d) Sound cannot travel through vacuum whereas light can.
Answer:
(c) Light travels much faster than sound.