AP State Board new syllabus 8th Class Physics Guide 5th Lesson Sound Textbook Exercise Questions and Answers.
AP 8th Class Physical Science 5th Lesson Questions and Answers Sound
8th Class Physics 5th Lesson Sound Questions and Answers (Exercise)
Question 1.
Choose the correct answer.
Sound can travel through
a) gases only
b) solids only
c) liquids only
d) solids, liquids and gases.
Answer:
(d) solids, liquids and gases.
Question 2.
Voice of which of the following is likely to have minimum frequency?
a) Baby girl
b) Baby boy
c) A man
d) A woman
Answer:
(b) Baby boy
Question 3.
In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.
a) Sound cannot travel in vacuum. (T/F)
Answer: True
b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
Answer: False
c) If the amplitude of vibrations is large, sound is feeble. (T/F)
Answer: False
d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
Answer: True
e) The lower the frequency of vibration, the higher is the pitch. (T/F)
Answer: False
f) Unwanted or unpleasant sounds termed as music (T/F)
Answer: False
g) Noise pollution may cause partial hearing impairment. (T/F)
Answer: True
Question 4.
Fill in the blanks with suitable words.
a) Time taken by an object to complete one oscillation is called …………
b) Loudness is determined by the ………… of vibration.
c) The unit of frequency is …………
d) Unwanted sound is called …………
e) Shrillness of a sound is determined by the ………… of vibration.
Answer:
a) time period
b) amplitude
c) hertz ( Hz)
d) noise
e) frequency
Question 5.
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
Given that
Number of oscitation =40
Total time taken =4 seconds
Question 6.
The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Answer:
Number of vibrations per second =500
Time period = \(\frac{\text { total time }}{\text { number of vibrations }}=\frac{1}{500}\) = 0.002 seconds
Question 7.
Identify the part which vibrates to produce sound in the following instruments.
Answer:
- Stretched membrane
- String of Sitar
- Air column
Question 8.
What is the difference between noise and music? Can music become noise sometimes?
Answer:
Difference between noise and music are as follows.
Noise | Music |
It is unpleasant sound | It is pleasant sound |
It leads to noise pollution | No such pollution takes place |
It is hazardous to health | It is good for health |
No special instruments are required to produce noise | Special instruments are required to play music |
Yes, music becomes noise some times, when it crosses the bearable range of sound for the ears.
Question 9.
List sources of noise pollution in your surroundings.
Answer:
As we know, noise pollution is caused by excessive sound in our surroundings. The sources of this excessive sound are as follows:
- Sounds of vehicles
- Sounds of bursting of crackers and explosives,
- Sounds of loudspeakes, TVs, transistors,
- Sounds of kitchen appliances,
- Sounds of desert coolers, air conditioners etc.
Question 10.
Explain in what way noise pollution is harmful to human.
Answer:
Presence of excessive noise in the surroundings which are irritating and unacceptable, may cause many health related problems.
e.g:
- Lack of sleep
- Hypertension
- Anxiety
- Temporary or permanent impairment of hearing.
Question 11.
Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer:
I will suggest my parents to buy the house which is three lanes away from the roadside. This is because the house on the roadside will receive the unwanted sounds of vehicles whereas the house which is three lanes away from the roadsides will be free from noise pollution.
Question 12.
Sketch larynx and explain its function in your own words.
Answer:
In humans, the sound is produced by the voice box also called larynx. We can easily feel this part of the body by putting our fingers on the throat and find a hard bump that seems to move when we swallow.
Structure :
- It is upper end of the wind pipe.
- Two vocal cords are stretched across the voice box or larynx.
- The two vocal cords, are stretched across the larynx in such a manner that it leaves a narrow slit between them for the passage of air.
Working :
- When the lungs force air through the slit, the vocal cords vibrate and hence producing sound.
- Muscles attached to the vocal cords can make the cords tight or loose.
- When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.
Question 13.
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:
Light travels at the speed 3 × 108 m/s while sound travels at a speed of 332 m/s i.e., light travels much faster than sound. That is why, lightning is seen earlier and thunder is heard later.
Extended Learning – Activities and Projects
Question 1.
Visit the music room of your school, You may also visit musicians in your locality. Make a list of musical instruments. Note down the part of these instruments that vibrate to produce sound.
Answer:
a) Flute — Air column
b) Tabala — Membrane
c) Harmonium — Metal reeds
d) Sitar — String
e) Veena — String
f) Drum — Membrane
g) Guitar — String
f) Violin — String
Question 2.
If you play a musicial instrument, bring it to the class and demonstrate how you play it.
Answer:
Student Activity
Question 3.
Prepare a list of famous Indian musicians and the instruments they play.
Answer:
a) Ravi Shankar — Sitar
b) Amjad Ali Khan — Sitar
c) Zakir Hussain — Tabala
d) Alla Rakha — Tabala
e) Hari Prasad Chaurasia — Flute
f) Panna Lal Ghosh — Flute
g) Bismilla Khan — Sehnai
Question 4.
Take a long thread. Place your hands over your ears and get some one to place this thread round your head and hands. Ask her to make the thread taut and hold its ends in one hand. Now ask her to draw her finger and thumb tightly along the thread as shown in figure. Can you hear a rolling sound like that of a thunder? Now repeat the activity while another friend stands near both of you. Can he hear any sound?
Answer:
Yes
Question 5.
Make two toy telephones. Use them as shown in Figure. Make sure that the two strings are taut and touch each other. Let one of you speak. Can the remaining three persons hear? See how many more friends you can engage in this way. Explain your observations.
Answer:
Yes, they can hear as the sound travels through string. We can engage as many friends as we wish.
Question 6.
Identify the sources of noise pollution in your locality. Discuss with your parents, friends and neighbours. Suggest how to control noise pollution. Prepare a brief report and present it in the class.
Answer:
Sources of noise pollution are
- Vehicles on road.
- Sound from construction sites.
- Sound from radio, TV, tape recorders etc.
- Sound from factories.
- Sound from fire crackers.
To control noise pollution :
- The noisy operations must be conducted outside the residential areas.
- TV, Radio etc. should be run at lower volumes.
- Use of loudspeakers should be minimised.
- Plantation should be done on road side.
8th Class PS 5th Lesson Questions and Answers (Lab Activities)
Activity – 1
Take a metal plate (or a pan). Hang it a convenient place in such a way that it does not touch any wall. Now, strike it with a stick. Also, touch the plate or pan gently with a finger. We feel vibration for sometime.
Now again, strike the plate with the help of stick and hold it tightly with hands immediately after striking. Here, we cannot hear the sound.
Observation : Now, gently touch the plate after it stops producing sound. Here, there is no sensation of vibration on the fingers.
Conclusion : So, we conclude from the activity that sound is produced by vibrating a body or thing.
Activity – 2.
Take a rubber band, put it around the longer side of a pencil box. Insert two pencils between the box and the stretched rubber. Now, pluck the rubber band somewhere in the middle.
Observation : Here, we find that if a tightly stretched rubber band is plucked, then it vibrates and produces sound and if its vibration stops, then it does not produce any sound.
Conclusion : We conclude that the vibrating object produces sound.
Activity – 3
Take a metal dish and pour water inside it. Strike it at its edge by a spoon. We hear some sound. Again, strike the plate and then touch it. Here, we feel that the dish is vibrating. Now, strike the dish again and again observe on the surface of water.
Observation : Here, we notice some waves on the water surface.
Conclusion : The vibrating object produces sound. In some cases the vibrations are easily visible to us and imost cases, their amplitude is too small that we cannot see them. However, we can feel them.
Activity – 4
Take a hollow coconut shell and make a musical instrument ‘ektara’. It can also be made with the help of an earthen pot. Now, play this instrument and identity its vibrating part.
Here, we come to the conclusion that the vibrating part of the musical instrument ‘Ektara’ is a stretched string.
Activity – 5
Take 6 to 8 metal bowls or tumblers. Fill the water in them upto different levels which increases gradually from one end to the other. Now, take a pencil and gently strike the bowls. Strike all of them one by one and it will produce a pleasant sound. This is our Jaltrang.
Observation: We hear a pleasant sound due to the difference in frequencies.
Conclusion: We conclude that as the amount of water in the tumblers goes on increasing, the frequency of sound produced also goes on increasing.
Activity – 6
Take two rubber strips of the same size and place these two pieces one above the other and make stretch tight. Now, blow air through the gap between them. So, as the air blows through the stretched rubber strips, then a sound is produced. We can also take, a piece of paper with a narrow slit and hold it between the fingers.
Observation : Blow through the slit and try to listen the sound.
Conclusion : Our vocal cords produce sound in a similar manner.
Activity – 8
Take a bucket or a bathtub. Fill it with clean water. Take a small bell in one hand. Shake this bell inside the water to produce sound. Make sure that the bell does not touch the body of the bucket or the tub.
Now, gently place your ear on the water surface and try to listen some sound. Be careful water should not enter to ear.
Observation : Here, we find that some sound is heard.
Conclusion : We conclude that sound can travel through liquids.
Activity – 9
Take a metre scale or a long metal rod and hold its one end to your ear. Ask your friend to gently scratch or tap at the other end of the scale.
Here, we hear the sound of scratch. So, if someone is away from us and willing to listen the sound of scratch, then he will not be able to listen.
Also, we can perform the above activity by placing our ear at one end of along wooden or metallic table. Now, ask to your friend to gently scratch the other end of table.
Observation : Here, we find that sound can travel through wood or metal.
Conclusion : Sound can travel through any solid.
Activity – 10
Take a plastic or tin – can and cut its both the ends. Now, stretch a piece of thin rubber sheet across one end of can and fasten it with a rubber band and put four or five grains of dry cereal (like wheat) on the stretched rubber. Now ask your friend to speak ‘Hurrey, Hurrey’ from the open end.
Observation : We will notice that when the sound of ‘Hurrey, Hurrey’ falls on the rubber sheet from below, then the grains placed over it starts jumping up and down indicating thevibrations of rubber sheet.
Conclusion : This is to demonstrate that how the working of the eardrum in our ear works.
Activity – 11
Take a metallic tumbler and a tablespoon. Also tie a small thermocol ball to a thread and suspend it in such a way that it touches the rim of tumbler.
First of all, strike the tumbler gently with a spoon. Try to hear a feeble sound and at the same time, the suspended thermocol ball is pushed away to a small distance by vibrating tumbler. So, when the amplitude of vibration of tumbler is small, the sound produced is feeble.
Observation : Now, strike the tumbler at the rim with the spoon. Try to hear a very loud sound and at the same time, the suspended thermocol ball is pushed away to a large distance by the vibration of tumbler.
Conclusion : When the amplitude of vibration of tumbler is large, the sound produced is very large. The loudness of sound depends on the amplitude of vibration of sound producing object.