Question:
Suppose you and your friend are on the Moon. Will you be able to hear any sound produced by your friend?
Answer:
No we will not hear any sound on the Moon. The Moon does not have any atmosphere, since sound is a mechanical wave and requires a medium to travel.
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 3.
What propagates along with the waves ?
Q 4.
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 5.
How are the wavelength and frequency of a sound wave related to its speed ?
Q 6.
How are compressions and rarefactions produced near a source of sound ?
Q 7.
How is sound propagated through a material medium ? What is wave motion ?
Q 8.
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 9.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 10.
What are the factors speed of sound wave depends upon?
Q 11.
Explain the working and application of a sonar.
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.
What is a mechanical wave?
Q 14.
If 20 waves are produced per second, what is the frequency in hertz?
Q 15.
What is reverberation?
Q 16.
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 17.
An engine is approaching a hill at constant speed.When it is at a distance of 0.9 km,it blows a whisde,whose echo is heard by the driver after 5 s.If the speed of sound is 340 m/s,calculate the speed of the engine.
Q 18.
sonar emits pulses on the surface of water which are detected after reflection from its bottom at a depth 1531 m.If the time interval between the emission and detection of the pulse is 2 s,find the speed of : sound in water.
Q 19.
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 20.
Why transverse wave does not travel through air or gases?
Q 21.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 22.
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 23.
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 24.
Why are sound waves called mechanical waves ?
Q 25.
What is audible range ?
Q 26.
What is sonic boom and when is it heard ?
Q 27.
Try to imagine what you would feel, what sort of person you would be,had you been born totally deaf.
Q 28.
What is a longitudinal wave?
Q 29.
Give an application use of ultrasonics.
Q 30.
By how much does the speed of sound increase with rise of temperature ?
Q 31.
Why do we use upholstered seats in theatres and halls ?
Q 32.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 33.
Fill in the blanks :
Number of oscillations completed by the oscillator in one second is known as ___________.
Q 34.
Fill in the blanks :
Ripples waves on water surface are example of ____________.
Q 35.
Fill in the blanks :
Sound, compressional waves in springs are examples of _____________.
Q 36.
Fill in the blanks :
Full form of SONAR is __________________________.
Q 37.
Fill in the blanks :
v = ? × ?
Q 38.
What is Sound? Why it is important for us?
Q 39.
Why sound waves are called mechanical waves?
Q 40.
What type of waves can travel in vacuum? Give example(s).
Q 41.
What is speed of sound in air?
Q 42.
Write differences between Transverse waves and Longitudinal waves.
Q 43.
What are ultrasonics?
Q 44.
Which wave characteristics determine the
(a) Loudness (b) pitch of sound?
Draw two different waveforms and mark these characteristics on it.
Q 45.
Demonstrate an activity to show that sound requires a medium to travel.
Q 46.
Guess which sound has a higher pitch: guitar or car horn?
Q 47.
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 48.
Distinguish between loudness and intensity of sound.
Q 49.
What is the audible range of the average human ear ?
Q 50.
Can sound waves travel through vacuum ?
