Propagation of Sound is a chapter in the Class 8th Science book. It talks about sound and its effects. It discusses how sound is produced and terms associated with it: Amplitude. time period, frequency, the range of audible sound in humans i.e. 20 Hz to 20000 Hz.
Propagation of Sound NCERT Solutions
1. Choose the correct answer.
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases
Ans 1: d) Solid. liquids and gases
Question 2: Voice of which of the following is likely to have a minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
Ans 2: c) A man
Also Read: Cell Structure and Functions NCERT Solutions
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 a vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
(g) Noise pollution may cause partial hearing impairment. (T/F)
Ans 3:
a) True: Sound needs a medium to travel
b)False- The number of oscillations per second of a vibrating object is called Frequency.
c) False If the amplitude of vibration is large sound will be more.
d) True, the audible range of human ear is 20Hz to 20000 Hz.
e) The statement is False. Frequency is directly proportional to Pitch. High frequency means higher pitch.
f) False: Unwanted sound is termed as noise. Music can not be unpleasant.
g) Yes, it’s true. Excessive and regular noise exposure can cause hearing impairments.
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.
Ans 4:
a) Time Period
b) Amplitude
c) Unit of frequency is Hertz (Hz)
d) Unwanted sound is called Noise
e) Frequency of vibration
Question 5: A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency
Ans 4:
Frequency = Total number of oscillations per second
Frequency = 40 /4
=10 Hz
Time period = 1/Frequency
= 1/10
= 0.1 s
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?
Ans 6: Frequency means the number of oscillations per second.
Frequency = 500 Hz
Time Period = 1/500
= 0.2 s
Question 7: Identify the part which vibrates to produce sound in the following instruments.
(a) Dholak
(b) Sitar
(c) Flute
Ans 7:
a) Dholak has a membrane on the top. When the dholak is hit then this membrane vibrates and produces sound that we hear.
b) Sitar has strings in it. When a sitar player plucks the strings then the vibration of the strings produces sound. That’s how the player is able to produce a beautiful sound.
c) Flute has holes in it. When we blow air in the flute then the vibration is caused by the movement of the air.
Question 8: What is the difference between noise and music? Can music become noise sometimes?
Ans 8: Anything that is unpleasant to hear is noise. A sound which is soothing can be called as music. Yes, music can sometimes become noise when it is too loud and fast. A sound track can be music for someone and the same music can be noise for those who hate such music.For ex. sounds played in loudspeaker can be unpleasant. So they act as noise.
Question 9: List sources of noise pollution in your surroundings.
Ans 9: Sources of noise pollution in our surroundings are:
Loudspeakers played in localities
Washing machine sound in a neighbouring house.
Sound of vehicles
Sounds from nearby factories
Question 10: Explain in what way noise pollution is harmful to human.
Ans 10: Noise pollution is harmful to humans because it can cause various issues like:
Hearing impairments
Excessive noise can cause headache
Lack of concentration
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.
Ans 11: We would advise our parents to buy the house that is away from the road because it will have less noise from the road as compared to the one that is one the roadside. Many vehicles will pass from the road that will cause noise the whole day. So, it is better to buy a house that is away from the road.
Question 12: Sketch larynx and explain its function in your own words.
Ans 12: The larynx contains vocal cords that produce the sound when we speak. Air passes through the gap between the vocal cords. Air is pushed upwards by lungs when we try to speak. This movement produces sound when we speak. Hence, the larynx is very important.
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?
Ans 13: Though Lightning and thunder take place in the sky at the same time we can see the lightning first and the thunder sound is heard later. This is because the speed of light is higher than the speed of the sound.
So these were the accurate answers for Propagation of Sound NCERT Solutions for Class 8 Science. This was your teacher and guide, Deepak Kumar here. Stay connected to Careeradvice4u for more Class 8 NCERT Solutions for other chapters.
- DAV Class 7 Science Solutions With Explanations: All Chapters - February 6, 2022
- Pollution of Water Question Answers | DAV Class 8 Science - February 4, 2022
- Fabric from Fibre Solutions | DAV Class7 Science Chapter 14 - January 25, 2022
Leave a Reply