Question:
What is a wave number?
Answer:
The number of wavelengths present per unit length is called wave number. i.e. it is the reciprocal of wavelength = 1/?.
Sound
Q 1.
What are the factors speed of sound wave depends upon?
Q 2.
Fill in the blanks :
v = ? × ?
Q 3.
Explain how sound is produced by your school bell ?
Q 4.
What propagates along with the waves ?
Q 5.
Why do we use upholstered seats in theatres and halls ?
Q 6.
Explain how the human ear works.
Q 7.
Radio Ceylon broadcasts at 25 m.What is the frequency of the station ?
Q 8.
What is a sonic boom ?
Q 9.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 10.
What is the audible range?
Q 11.
Fill in the blanks :
Loudness of sound is measured in ___________.
Q 12.
A bat emits ultrasonic sound of frequency 100 kHz in air.If this sound meets a water surface,what is the wavelength of (a) the reflected sound wave (b) the transmitted sound wave ?
Given speed of sound in air = 340 m/s and in water = 1486 m/s.
Q 13.
Draw a curve showing density or pressure variations with respect to distance for a disturbance produced by sound.Mark the position of compression and rarefaction on this curve.Also define wavelengths and time period using this curve.
Q 14.
What is acoustical transite ?
Q 15.
Try to imagine what you would feel, what sort of person you would be,had you been born totally deaf.
Q 16.
Why sound waves are called mechanical waves?
Q 17.
What is a wave number?
Q 18.
A sound wave travels at a speed of 339 ms
–1. If its wavelength is 1.5 cm, what is the frequency of the wave?
Q 19.
Distinguish between loudness and intensity of sound.
Q 20.
What is reverberation ? How can it be reduced ?
Q 21.
The sound of distant horses can be heard by applying the ear to the ground whereas it is inaudible if the ear is held a little distance above the ground.Explain.
Q 22.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 23.
Fill in the blanks :
Waves transport _________ not matter.
Q 24.
Fill in the blanks :
Sound having frequency less than 20Hz is known as ___________.
Q 25.
A ship sends out ultrasound that returns from the seabed and is detected after 3.42 s.If the speed of the ultrasound through sea water is 1531 m/s,what is the distance of the seabed from the ship ?
Q 26.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Q 27.
What is the audible range of the average human ear ?
Q 28.
is sound wave called a longitudinal wave ?
Q 29.
Explain how defects in a metal block can be detected using ultrasound.
Q 30.
What is the minimum distance of the obstacle from the source of sound for hearing distinct echo ?
Q 31.
Distinguish between music and noise.
Q 32.
We see flash earlier than the thunder.Discuss.
Q 33.
Deaf people can be made to dance to music.Explain how ?
Q 34.
What travels faster : a rifle bullet or the sound of the shot fired from it ?
Q 35.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 36.
Can sound wave travel in vacuum?
Q 37.
What type of waves can travel in vacuum? Give example(s).
Q 38.
Give examples of organisms which can hear infrasonic?
Q 39.
Calculate the wavelength of a sound wave having a frequency 300 Hz and speed 330 m/s.
Q 40.
A sound wave has a frequency of 2
kHz and wavelengtl 35 cm.How long will it take to travel 1.5 km ?
Q 41.
A person standing between two vertical cliffs and 680 m away from the nearest cliff,shouted.He heard the first echo after 4 s and the second echo 3 s later.Calculate (a) the speed of sound in air and (b) distance between the two cliffs.
Q 42.
A man standing at 51 m from a wall fires a gun.Calculate the time after which an echo is heard.The speed of sound is 340 m/s.
Q 43.
What are wavelength,frequency,time period and amplitude of a sound wave ?
Q 44.
Describe with the help of a diagram,how compressions and rarefactions are produced in air near a source of sound.
Q 45.
What are infrasonics ?
Q 46.
What is persistence of hearing ?
Q 47.
How can you make a building sound proof ?
Q 48.
How is sound propagated through a material medium ? What is wave motion ?
Q 49.
Discuss the structure of human ear from auditory aspect only.
Q 50.
Hearing may be damaged by excessive noise.So our ears sometimes need protection from continuous loud sound. Hearing damage depends on the sound intensity level (decibel level)and the exposure time,and the exact combinations vary for different people.Normally,at 90 dB,it takes 8 hours or less for the damage to receptor nerves to occur.Further,it is found that if the sound level is increased by 5 dB,the safe exposure limit is cut to half.
(a) How long will it take for a sound of a very loud lawn mower (or a motorcycle) of 95dB to damage the hearing ?
(b) What is the nonstop exposure time for a 105 dB sound to damage the ear ?
(c) What should be done to protect the society from the danger of losing the divine gift of hearing power ?
