Chapter 11 Sound Long Questions
Q.1 What is the necessary condition for the production of sound?
Q. 3 How can you prove the mechanical nature of sound by a simple experiment?
Q.4 What do you understand by the longitudinal wave? Describe the longitudinal nature of sound waves.
Q. 5 Sound is a form of wave. List at least three reasons to support the idea that sound is a wave.
Q.8 On what factors does the loudness of sound depend?
Q.11 What is difference between frequency and pitch? Describe their relationship graphically.
Q.13 If the pitch of sound is increased, what are the changes in the following?
a. the frequency b. the wavelength c. the wave velocity d. the amplitude of the wave
Q.16 Explain that noise is a nuisance.
Q.17 Describe the importance of acoustic protection.
Q.18 What are the uses of ultrasound in medicine?
Q.1 What is the necessary condition for the production of sound?
Answer: Sound wave can be produced by vibrating a body and travel in a medium whose particles can vibrate. The frequency of vibrations must be greater than 20Hz and Jess than 20,000Hz. In solids the sound waves have faster speed than in air or liquid due to larger elasticity.
Q.2 What is the effect of the medium on the speed of sound? In which medium sound travels more faster: air, solid or liquid? Justify your answer.
Answer: Sound waves arc mechanical waves so medium has effect on the speed of sound waves. In solids the sound waves have faster speed than in air or Liquid due to larger elasticity.
Q. 3 How can you prove the mechanical nature of sound by a simple experiment?
Answer: The sound waves are “mechanical waves”. It require material medium. It can be proved by placing an electric bell inside a glass jar where vacuum is produced. The working electric bell is made ON, but sound produced by it cannot be heard, due to vacuum and no material medium be present around it. While before producing vacuum sound will he heard.
Q.4 What do you understand by the longitudinal wave? Describe the longitudinal nature of sound waves.
Answer:
Longitudinal Waves: The waves are said to be longitudinal if the particles of the medium vibrate in the same direction as the direction of propagation of waves. Sound waves are mechanical and longitudinal in nature. It means the particles of the medium (air, liquid or solid) vibrate in the same direction as the direction of the sound waves travel.
Q. 5 Sound is a form of wave. List at least three reasons to support the idea that sound is a wave.
Answer:
Sound is a form of wave.
- It gives the sensation of hearing. If we listening sound the membrane of our ear starts vibrating.
- Ultra-sounds (high energy waves) are used in medical sciences.
Q. 6 We know that waves manifest phenomenon of reflection, refraction and diffraction. Does sound also manifest these characteristics?
Answer: Yes, sound waves also exhibit the characteristics like reflection, diffraction and refraction.
Echo is the practical example for the reflection of sound waves.
Listening of the person in other room is an example of diffraction of sound waves.
There are example to show the refraction of sound waves by which their speed and direction is change.
Q.7 What is the difference between the loudness and intensity of sound? Derive the relationship between the two.
Answer:
Loudness: The magnitude of “auditory sensation” due to sound waves is called loudness. Faint and loud voice can be distinguished by the magnitude of loudness.
Intensity of sound: The energy transferred by sound waves per unit area per second. When unit area in at 900 to direction of propagation of sound waves, is called intensity of sound. Its unit are “watt per square meter”.
Relation between loudness and Intensity:
The audible sound waves for a normal human ear have intensity ranging from 10-12 Wm-2 to 1Wm-2. it is a very large range; therefore it is scaled in powers of ten.
Power of ten:
The lowest intensity to which ear can response is 10-12 Wm-2. It is taken as reference value and is written as zero bel. Therefore on bel intensity is 10-11 Wm-2 or it is equal 10db (decibel).
Experimentally it is confirmed that loudness is directly proportional to logarithm of intensity value we can write as
L ∝ log I
L = (constant) log I
L = k log I
Here k is constant of proportionality which is called proportionality constant.
Q.8 On what factors does the loudness of sound depend?
Answer:
Loudness: Loudness is the characteristic of sound by which loud and faint sounds can be distinguished.
Factors on which loudness depends upon:
a. Amplitude of vibrating body.
b. Area of vibrating body.
c. Distance from vibrating body.
Q.9 What do you mean by the term intensity level of the sound? Name and define the unit of intensity level of sound.
Answer:
Intensity of Sound: Sound energy passing per second through a unit area held perpendicular to the direction of propagation or sound waves is called intensity of sound.
Unit: Its unit is watt per square metre (Wm-2)
Q.10 What are the units of loudness? Why do we use logarithmic scale to describe the range of the sound intensities we hear?
Answer:
Unit of loudness: Decibel is the unit of loudness (dB)
Why do we use logarithmic scale to describe the range of the sound intensities we hear?
It’s because the ear responds to sound intensity logarithmically. And in turn that’s because nature produces sound intensities over an extremely wide range – if our ears could not cope with that range, there would be little purpose in having ears.
Q.11 What is difference between frequency and pitch? Describe their relationship graphically.
Answer: The number of wave lengths passing through a point in one second is called frequency. Its units are hertz (HZ) and, the pitch is quality of sound due to which a shrill and grave voice can be distinguished. The greater is frequency of sound, the larger is pitch of sound and vice-versa.
Q.12 Describe the effect of change in amplitude on loudness and the effect of change in frequency on pitch of sound.
Answer: The effect of change of amplitude of sound waves the energy changes and due to which loudness may also change.
The magnitude of sensation of sound is called “loudness”. When frequency of sound wave effect the pitch of sound waves. The greater is frequency, the larger is it pitch and vise-versa.
Q.13 If the pitch of sound is increased, what are the changes in the following?
a. the frequency b. the wavelength
c. the wave velocity d. the amplitude of the wave
Answer: Its frequency will be increased.
Q.14 If we clap or speak in front of a building while standing at a particular distance, we rehear our sound after sometime. Can you explain how does this happen?
Answer: It is due. to the reflection of sound waves. After incident on the walls of they come back into the same medium. That is why we rehear the sound after some time. It is called echo.
Q. 15 What is the audible frequency range for human ear? Does this range vary with the age of people? Explain.
Answer: Sound in the form of continuous note, have audible frequency range from 20Hz to 20,000Hz. This means that a normal human ear cannot hear sound wave having frequencies less than 20Hz and grater than 20,000Hz . This range of audible frequency is different fro ears of different persons. Also the width of this range of audible frequencies decreases with age. Young children can hear sound of 20,000Hz, but old people cannot hear sound even above 15000Hz.
Q.16 Explain that noise is a nuisance.
Answer: A noise nuisance is a noteworthy and unreasonable amount of sound from a neighboring premises. The nuisance could be coming from a domestic or commercial property and affects you and your life in a significant way which is more than a simple annoyance.
The main factors that officers and the courts will take into account are:
- time of day
- location
- duration of each individual noise event
- volume of the noise
- character of the noise
- frequency with which noisy events occur
It is not necessary for officers to take noise readings to establish if a nuisance exists, although sometimes this can help. On the whole the judgement of an experienced and independent officer is enough to determine if a noise is unreasonable or not.
Q.17 Describe the importance of acoustic protection.
Answer: Acoustics is the study of waves, vibrations and sound and its most common applications lie in the sound and noise control industries. Acoustic protection is the application of soft and porous material to protect individuals against undesirable sounds and noises.
Q.18 What are the uses of ultrasound in medicine?
Answer: In medicine, ultrasound is used to detect changes in the appearance of organs, tissues, and vessels and to detect abnormal masses, such as tumors. In an ultrasound exam, a transducer both sends the sound waves and records the echoing waves.