Sound Class 8 Extra Questions and Answers

These AP 8th Class Physics Important Questions and 5th Lesson Sound Class 8 Extra Questions will help students prepare well for the exams.

Class 8 Science Sound Extra Questions

Sound Class 8 Important Questions

Question 1.
What is Sound ? How does sound produces ?
Answer:
Sound is a type of energy that makes us hear. A vibrating body produces sound.

Question 2.
What is Vibration ?
Answer:
The to and fro motion of an object is called vibration.

Question 3.
Do all bodies produce sound ?
Answer:
Yes, all bodies produce sound except in vacuum.

Question 4.
Which two properties of sound help us to recognise it ?
Answer:
Frequency and amplitude.

Question 5.
Which animal can hear sound of frequencies higher than 20,000 Hz ?
Answer:
Dogs, cats.

Question 6.
What do you feel when you touch a sound producing body ?
Answer:
When we touch a sound producing body, we feel vibrations.

Question 7.
Does any part of our body vibrate when we speak ? Name the part.
Answer:
Yes, larynx (vocal cords)

Question 8.
Name two musical instruments which produce sound by vibrating strings ?
Answer:
Sitar and Ektara.

Question 9.
We have learnt that vibrations is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us ?
Answer:
If the sound produced by a vibrating body is in the audible range, the sound produced will be heard by us otherwise we will not be able to hear the sound even though the body is vibrating.

Question 10.
Suppose a stick is struck against a frying pan in vacuum will the frying pan vibrate? Will we be able to hear the sound ? Explain.
Answer:
The frying pan will vibrate. We will not be able to hear the sound of vibration because sound cannot travel in vaccum.

Question 11.
What is the normal length of vocal cords in man ?
Answer:
The normal length of the vocal cord of a man is about 20 mm long.

Question 12.
What is necessary for the propagation of Sound ?
Answer:
Sound needs a medium to travel.

Question 13.
In which type of medium liquids, solids or gas, sound can move ?
Answer:
A sound can make in all the three types of mediums.

Question 14.
Two astronauts are floating close to each other in space. Can they talk to each, other without using any special device ? Give reasons.
Answer:
No, in space there is vacuum and sound cannot travel in vacuum.

Question 15.
What is called time period ?
Answer:
It is time taken by a vibrating body to complete one oscillation.

Question 16.
Define freqency.
Answer:
The number of oscillations that a pendulum undergoes in a unit time is called frequency.

Question 17.
Define Hertz.
Answer:
It is the unit of frequency. Frequency of a vibration or oscillation is measured in hertz.

Question 18.
Why are some sounds loud ?
Answer:
The sounds which have greater amplitude are louder.

Question 19.
What is a music ?
Answer:
Music is a combination of sounds that are produced in an order and pleasant to hear.

Question 20.
What is a noise ?
Answer:
The sounds which are not pleasant to hear is called a noise.

Question 21.
What is pitch?
Answer:
The shrillness of sound is known as pitch.

Question 22.
What is audible sounds ? What is audible range ?
Answer:
The sounds that a sound normal human being can hear is called audible sounds. Frequency of audible sound ranges from 20 to 20,000 Hz.

Question 23.
A bird makes high pitch sound and a lion makes a low pitch roar. Which one produce sound of more frequency ?
Answer:
The bird produces sound of more frequency because it has high frequency as we already know pitch depends upon frequency.

Question 24.
Why do we produce sounds with different pitches or amplitudes while speaking ?
Answer:
The vibration in pitch and amplitude of sound during our speech helps us to communicate with others in from of language.

Question 25.
Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why ?
Answer:
The speed of light is more than speed of sound. So light travels faster. Therefore we can see lightning first and then we can hear thunder.

Question 26.
What is the unit to measure the sound intensity ?
Answer:
Decibel is the unit and to measuring the intensity of sound. It is denoted as dB.

Question 27.
Pendulum A makes 14 oscillations in five seconds and pendulum B makes 10 oscillations in three seconds. Which has a higher frequency ? Express the frequency of each pendulum is hertz.
Answer:
Frequency of A = \(\frac{14}{5}\) = 2.8 hertz
Frequency of B = \(\frac{10}{3}\) = 3.33 hertz
Pendulum B has higher frequency.

Question 28.
Lightning can be seen the moment it occurs. Ravi observes lightning in his area. We hears the sound 5 sec after he observed lightning. How far is he from the place where lightning occurs ? (speed of sound = 330 m/s)
Answer:
Distance = speed × time
= 330 m/sec × 5 sec = 1650 m

Question 29.
A simple pendulum makes 10 oscillations in 20 seconds. What is the time period and frequency of its oscillation ?
Answer:
Time period = \(\frac{\text { Time }}{\text { No.of oscillations }}\) = \(\frac{20}{10}\) = 2 sec.
Frequency = \(\frac{\text { No.of oscillations }}{\text { Time }}\) = \(\frac{10}{20}\) = 0.5 Hz.

Question 30.
Among water and steel, in which medium will the sound wave travel faster ?
Answer:
The sound will travel faster in steel because speed of sound is fastest in solids.

Question 31.
Why do we not hear the sound of an explosion on the surface of the Moon ?
Answer:
There is no atmophere on the moon and sound waves need a medium to travel, so we cannot hear the sound on the moon.

Question 32.
How do whales and dolphines hear sound ?
Answer:
Through water as a liquid medium, both whales and dolphins hear the sound.

Question 33.
Explain why babies have feeble sound ?
Answer:
Due to the small amplitude of their sound, babies have feeble sound.

Question 34.
Different bees produce buzzing sounds of different pitches, which affects the pitch of the bee’s buzzing sound ?
Answer:
The faster the bee vibrates the wings, the greater the freqeuncy of the sound.

Question 35.
What is the difference between pitch and frequency ?
Answer:
Pitch is perceptual to sensation. Freqency is a physical quantity that can be measured.

Question 36.
What is the frequency of wave with time period 0.025 sec. ?
Answer:
T = 0.025 sec.
? = \(\frac{1}{T}\) = \(\frac{1}{0.025} = 40 Hz\)

Question 37.
What is ultrasound ?
Answer:
Ultrasound refers to sound that has a frequency above the audible range (20,000 Hz) of the human ear.

Question 38.
Two astronauts are walking on the moon which has no atmosphere. They are talking to each other normally, without using any device. Will they be able to hear one another ? Justify your answer.

1. No, they cannot hear one another.
2. Propagation of a sound requires a medium.
3. There is no medium that exists as no atmosphere on the moon.
4. Hence sound cannot propagate on the moon.

Sound Extra Questions

Question 1.
What are the differences between the noise and music ? Explain.
Answer:

Noise	Music
1. Sounds which are not pleasant to hear are called Noise.	1. Sounds which are pleasant to hear are called Music.
2. Noise is an irregular combination of sounds.	2. Music is a combination of sounds which are produced in order.
3. It is unpleasant to hear.	3. It is pleasant to hear.

Question 2.
How is sound produced in humans ?
Answer:
In humans, voice box or the larynx is the most important source of sound. Two ligaments, known as vocal cords, are stretched across the larynx in such a way that it leaves a narrow slit between them for the passage of air. When the lungs force air through the slit, the vocal cords vibrate, producing voice.

Question 3.
Define vocal cords.
Answer:
These are the two ligaments stretched across the larynx in such a way that it leaves a narrow slit between them for passage of air.

Question 4.
How the muscles attached to vocal cords regulate sound ?
Answer:
Muscles attached to the vocal cords may make the cords tight or loose. When the vocal cords are tight and thin, the type or quality of voice is different fom that when these are loose and thick.

Question 5.
Why are the voice of men, women and children different ?
Answer:
The vocal cords in men are about 20mm long. In women these cords are about 5 mm shorter in respect to men. Children have very short vocal cords. This is the reason that the voice of men, women and children are different.

Question 6.
Why do our steps not produce loud sound if we walk on a carpet floor ?
Answer:
When we walk on a carpet floor, the amplitude of vibrations of the floor is reduced and the sound of our steps become feeble.

Question 7.
List three sources of noise pollution in your locality.
Answer:
Sources of noise pollution are :

1. Horn of vehicles.
2. Loud speakers of temples.
3. Generators running without silencers.

Question 8.
What are the harmful effects of noise pollutions ?
Answer:
Presence of excessive noise in the surroundings many cause many health related problems. Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution. A person who is exposed to a loud sound continuously may get temporary or even permanent deafness.

Question 9.
Suggest three measures to limit noise pollution in your locality.
Answer:
The measures to limit noise pollution in our locality are given here.

1. The industries which produce noise should be set up away from the residential areas.
2. The televison and the music systems should be run at low volumes.
3. The aircraft engines, transport vehicles, industrial machines and home appliances must be installed with silencing devices.

Question 10.
Suggest three measures to limit noise pollution in your locality.
Answer:

1. Trees must be planted along the roads and around the buildings.
2. Use of horns should be minimised.
3. Silencers must be installed in transport vehicles and industrial machines.

Question 11.
Compare the sound of drum and whistle.
Answer:
The frequency determines the shrillness or pitch of a sound. A drum vibrates with low frequency. Therefore, it produces low pitched sound. Whistle has a high frequency and therefore, produces a sound of higher pitch.

Question 12.
We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us.
Answer:
Since, range of vibrations is different by different objects. But we can hear the vibration which are less between 20 Hz to 20,000 Hz. So, sound of every vibration cannot be heard by us.

Question 13.
Briefly explain total hearing impairment.
Answer:
Hearing impairment means a person has damaged hearing ability and cannot hear properly. There are some people who born with poor hearing ability. A person with very poor hearing ability is said to be deaf. So, deafness is total hearing impairment.

Question 14.
We have a stringed musical instrument. The string is plucked in the middle first with a force of greater magnitude and then with a force of smaller magnitude. In which case would the instrument produce a louder sound ?
Answer:
It will create more loud sound in case of string stretched with a greater force because amplitude is greater in this case and loudness depends on the amplitude. Greater will be the loudness, greater will be the amplitude.

Question 15.
Two friends are playing with a toy telephone. Which of the points P, Q, R will vibrate if one of the Mends speaks into the cup ? Justify your answer.

Answer:

1. All the points P, Q and R will vibrate if one of the friends speaks into the cup.
2. Sound travels through the thread (a solid) and reaches another end by the vibration of particles in the thread.

Question 16.
Give a scientific explanation for the following.
Wood is not used to make bells.
Answer:

1. Sound is produced by vibrating body.
2. We use the bells to make sound.
3. Wood does not produce sound because it is not a vibrating body.
4. So wood is not used to make bells.

Extra Questions of Sound Class 8

Question 1.
Ravi Said “Vibrating objects produce sound”. Establish that the given statement is true with relevant example from your surroundings.
Answer:
The statement given by Ravi is correct.
1) Eg: 1) If we ring the bell in the school, sound will produce.
2) If we touch the bell while ringing, vibrating will experience.

2) Eg: 1) We can observe sound coming from the engine of vehicle.
2) This is due to vibration of the engine.

3) Eg: 1) Musical instruments vibrates and produce sound.
2) If we pull the string of veena or guitar.
3) It will produce sound.

Question 2.
Based on the belpw information answer the following questions.
Answer:

Musical Instrument	Vibrating part producing sounds.
1. Veena	Stretching string
2. Tabla	Stretching membrane
3. Flute	Air column
4. Dholak	Stretched membrane
5. Sitar	Stretching string
6. Drum	Stretched membrane

a) Name the instruments which have vibrating part like a thin elastic rubber band.
Answer:
Tabala, Dholak, Drum.

b) What are the vibrating particles in the air column ?
Answer:
Air particles.

c) What is the difference between Tabala and Sitar in terms of how they produce sound ?
Answer:
In Tabala, stretched membrane vibrates and produce sound. Whereas in Sitar stretching string vibrates and produce sound.

d) How to produce different frequencies using a flute ?
Answer:
By closing holes of the flute with fingers (or) By changing length of the air column.

Question 3.
What is the unit of the loudness of sound ? Explain giving the loudness a few sounds.
Answer:
The loudness is expressed in a unit called decibel (dB). It is essentially a ratio of the actual loudness to some base loudness level. The base level is usually defined as the loudness of sound that the human ear can just perceive.

The following table gives some idea of the loudness of sound coming from various sources.
Normal breathing 10 dB
Soft whisper (at 5m) 30 dB
Normal conservation 60 dB
Busy traffic 70 dB
Average factory 80 dB
At 80 dB the noise becomes physically painful.

Question 4.
What is eardrum ? How does it play an important role in hearing ?
Answer:

1. We hear sound through our ears.
2. The shape of outer part- of ear is like a funnel.
3. When sound enters in it, it travels down a canal at the end of which a thin membrane is stretched tightly.
4. It is called eardrum. It performs an important function.
5. The eardrum is like a stretched rubber sheet. Sound vibrations make the eardrum vibrate.
6. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain. That is how we hear.

Question 5.
How is sound produced and how is it transmitted and heard by us ?
Answer:

1. Sound is produced when any object starts vibrating by any means.
2. There vibrations travel from the source all around the environment through the particles of the environment.
3. Thus, it reaches to the destination, i.e., our ear.
4. Now, it enters our ear and travels down a canal at the end of which a thin membrane is stretched tightly known as eardrum.
5. The eardrum sends vibrations to inner part of the ear and finally reaches to the brain and we hear the sounds.

Question 6.
An alarm bell is kept inside a vessel as shown in Figure. A person standing close to it can distinctly hear the sound of alarm. Now, if the air inside the vessel is removed completely, how will the loudness of alarm get aftected for the same person ?

Answer:
Initially, the person is able to hear the sound coming from air and from water distinctly. But after some time, when the air is completely removed from the bottle, the sound will pass through the water and then through the glass. So, the man will not hear through the sound which was coming through the air initially.

Question 7.
Explain in detail how sound travel slower than light.
Answer:
As we know that the speed of sound in air is about 340 m/s. and the speed of light in air is 300,000,000 m/s. It means that sound travels at a slow speed while light travels much faster than sound.

So, though sound may take a few seconds to travel a distance of a few hundred metres, light will take practically negligible time to reach a distance of even a few kilometres.

Eg: In the rainy season, the flash of lightning is observed first and the sound of thunder is heard a little latter.

It is because of the very high speed of light that we see that the flash of lightning first and it is due to comparatively low speed of sound that the thunder is heard a little later.