Question:
What is a mechanical wave?
Answer:
A mechanical wave is a disturbance that moves through a medium when the particles of the medium set neighbouring particles into motion. The particles vibrating in turn do not move forward but the disturbance is carried forward.
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 is sound propagated through a material medium ? What is wave motion ?
Q 7.
How are compressions and rarefactions produced near a source of sound ?
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.
What is a mechanical wave?
Q 10.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 11.
What are the factors speed of sound wave depends upon?
Q 12.
Explain the working and application of a sonar.
Q 13.
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 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.
Why are sound waves called mechanical waves ?
Q 20.
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 21.
Fill in the blanks :
Sound, compressional waves in springs are examples of _____________.
Q 22.
Why transverse wave does not travel through air or gases?
Q 23.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 24.
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 25.
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 26.
What is audible range ?
Q 27.
What is sonic boom and when is it heard ?
Q 28.
Try to imagine what you would feel, what sort of person you would be,had you been born totally deaf.
Q 29.
What is a longitudinal wave?
Q 30.
Why sound waves are called mechanical waves?
Q 31.
Give an application use of ultrasonics.
Q 32.
Which wave characteristics determine the
(a) Loudness (b) pitch of sound?
Draw two different waveforms and mark these characteristics on it.
Q 33.
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 34.
By how much does the speed of sound increase with rise of temperature ?
Q 35.
Why do we use upholstered seats in theatres and halls ?
Q 36.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 37.
Fill in the blanks :
Number of oscillations completed by the oscillator in one second is known as ___________.
Q 38.
Fill in the blanks :
Full form of SONAR is __________________________.
Q 39.
Fill in the blanks :
If the time interval between original sound and reflected sound is more than 1/10 second then original sound and reflected sound can be heard clearly. This reflected sound is known as _______.
Q 40.
Fill in the blanks :
v = ? × ?
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.
What type of wave is represented by density- distance graph?
Q 45.
What is the audible range of the average human ear ?
Q 46.
Can sound waves travel through vacuum ?
Q 47.
What is the minimum distance of the obstacle from the source of sound for hearing distinct echo ?
Q 48.
How can you show that sound waves are longitudinal waves ?
Q 49.
Distinguish between music and noise.
Q 50.
Deaf people can be made to dance to music.Explain how ?
