Question:
Why are sound waves called mechanical waves ?
Answer:
Waves which need a material medium for propagation are called mechanical waves.Since sound waves also need a material medium for propagation,these are called mechanical waves.Sound waves are called mechanical waves or elastic waves as these are produced in a deformable or elastic medium.Unlike electromagnetic waves,sound waves need a medium to sustain them. Mechanical waves are governed by Newton’s laws of motion.
Sound
Q 1.
A hospital uses an ultrasonic scanner to locate tumors in a tissue. What is the wavelength of sound in a tissue is which the speed of sound is 1.7 km/s. The operating frequency of the scanner is 4.2 MHz. (1MHz = 10
6 Hz).
Q 2.
Explain the working and application of a sonar.
Q 4.
What is reverberation?
Q 5.
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 6.
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 7.
How are the wavelength and frequency of a sound wave related to its speed ?
Q 8.
How can you show that sound waves are longitudinal waves ?
Q 9.
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 ?
Q 10.
Fill in the blanks :
If a body repeats its back and forth, to and fro or up and down motion along a certain path, about a fixed point, in a certain time interval then the motion of such objects is said to be _____________.
Q 11.
How are compressions and rarefactions produced near a source of sound ?
Q 12.
Fill in the blanks :
In a __________ wave the particles of the medium oscillate in a direction perpendicular to the direction in which the wave propagates.
Q 13.
A longitudinal wave is produced on a slinky.The frequency of the wave is 25 Hz and it travels at a speed of 20 cm/s. Find the separation between consecutive positions of maximum compressions.
Q 14.
How is sound propagated through a material medium ? What is wave motion ?
Q 15.
What is a longitudinal wave?
Q 16.
Why do we use upholstered seats in theatres and halls ?
Q 17.
What are wavelength, frequency, time period and amplitude of a sound wave?
Q 18.
What is infrasonic? Give an example.
Q 19.
Demonstrate an activity to show that sound requires a medium to travel.
Q 20.
The sonic boom of an aircraft has a time period of 0 00005 s.Calculate the frequency of the sound produced.
Q 21.
Distinguish between loudness and intensity of sound.
Q 22.
How is ultrasound used for cleaning ?
Q 23.
What propagates along with the waves ?
Q 24.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 25.
Can sound wave travel in vacuum?
Q 26.
What type of waves can travel in vacuum? Give example(s).
Q 27.
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 28.
Write differences between Transverse waves and Longitudinal waves.
Q 29.
A wave of wavelength 0-60 cm is produced in air and it travels at a speed of 300 m/s.Will it be audible ?
Q 30.
Why are sound waves called mechanical waves ?
Q 31.
What is audible range ?
Q 32.
What is acoustical transite ?
Q 33.
Discuss the role of medium in the propagation of sound.
Q 34.
We see flash earlier than the thunder.Discuss.
Q 35.
Deaf people can be made to dance to music.Explain how ?
Q 36.
Fill in the blanks :
Number of oscillations completed by the oscillator in one second is known as ___________.
Q 37.
Fill in the blanks :
Waves transport _________ not matter.
Q 38.
Fill in the blanks :
Audible sound range is _________ to _____________.
Q 39.
Fill in the blanks :
The distance between two consecutive compressions or two consecutive rarefactions is called the ______________.
Q 40.
What is speed of sound in air?
Q 41.
Among solids, liquids and gases sound travels faster in which medium?
Q 42.
How are the wavelength and frequency of a sound wave related to its speed?
Q 43.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 44.
If 20 waves are produced per second, what is the frequency in hertz?
Q 46.
Give an application use of ultrasonics.
Q 47.
What type of wave is represented by density- distance graph?
Q 48.
A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?
Q 49.
An observer standing at the sea coast observes 54 waves reaching the coast per minute.If the wavelength of a wave is 10 m,find the wave velocity.
Q 50.
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.
