Question:
Give two practical applications of reflection of sound waves.
Answer:
Megaphone and (ii) Ear trumpet.Refer to Art.6.22,Page 347.
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.
How is sound propagated through a material medium ? What is wave motion ?
Q 3.
By how much does the speed of sound increase with rise of temperature ?
Q 4.
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 5.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 6.
How are compressions and rarefactions produced near a source of sound ?
Q 7.
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 8.
Fill in the blanks :
Sound, compressional waves in springs are examples of _____________.
Q 9.
Fill in the blanks :
Ripples waves on water surface are example of ____________.
Q 10.
How are the wavelength and frequency of a sound wave related to its speed ?
Q 11.
Fill in the blanks :
Number of oscillations completed by the oscillator in one second is known as ___________.
Q 12.
Fill in the blanks :
v = ? × ?
Q 13.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 14.
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 15.
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 16.
Why are sound waves called mechanical waves ?
Q 17.
What is audible range ?
Q 18.
If 20 waves are produced per second, what is the frequency in hertz?
Q 19.
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 20.
What is the audible range of the average human ear ?
Q 21.
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 22.
What is Sound? Why it is important for us?
Q 23.
What is a mechanical wave?
Q 24.
What is speed of sound in air?
Q 25.
What type of wave is represented by density- distance graph?
Q 26.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 27.
Distinguish between music and noise.
Q 28.
What is a longitudinal wave?
Q 29.
What is a wave number?
Q 30.
Guess which sound has a higher pitch: guitar or car horn?
Q 31.
A man fires a gun towards a hill and hears its echo after 5 s.He then moves 340 m towards the hill and fires his gun again.This time he hears the echo after 3 s.Calculate the speed of sound.
Q 32.
Explain the working and application of a sonar.
Q 34.
Deaf people can be made to dance to music.Explain how ?
Q 35.
Fill in the blanks :
Waves transport _________ not matter.
Q 36.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 37.
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 38.
What are wavefronts?
Q 39.
Suppose you and your friend are on the Moon. Will you be able to hear any sound produced by your friend?
Q 40.
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 41.
Write differences between Transverse waves and Longitudinal waves.
Q 42.
Which wave characteristics determine the
(a) Loudness (b) pitch of sound?
Draw two different waveforms and mark these characteristics on it.
Q 43.
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 44.
How does the sound produced by a vibrating object in a medium reach your ear ?
Q 45.
Explain how sound is produced by your school bell ?
Q 46.
Explain how defects in a metal block can be detected using ultrasound.
Q 47.
Explain how the human ear works.
Q 48.
What is sound barrier ?
Q 50.
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.
