Question:
Establish the relationship between speed of sound,its wavelength and frequency.If velocity of sound in air is 340 m/s,calculate:
(i) wavelength when frequency is 256 Hz.
(ii)frequency when wavelength is 0.85 m.
Answer:
Refer to Art.6.11,Page 330.
As v = v λ,λ===1.33 m.
As v = v λ,λ==400 Hz.
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 are compressions and rarefactions produced near a source of sound ?
Q 6.
Fill in the blanks :
Ripples waves on water surface are example of ____________.
Q 7.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 8.
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 9.
Fill in the blanks :
Sound, compressional waves in springs are examples of _____________.
Q 10.
How are the wavelength and frequency of a sound wave related to its speed ?
Q 11.
What is audible range ?
Q 12.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 13.
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 14.
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 15.
Fill in the blanks :
Number of oscillations completed by the oscillator in one second is known as ___________.
Q 16.
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 17.
Why are sound waves called mechanical waves ?
Q 18.
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 19.
Fill in the blanks :
v = ? × ?
Q 20.
What is Sound? Why it is important for us?
Q 21.
What type of wave is represented by density- distance graph?
Q 22.
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 23.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 24.
What is a mechanical wave?
Q 25.
Three persons, A, B and C are made to hear a sound travelling through different mediums as given below:
| Persons | Medium |
| A | Iron Rod |
| B | Air |
| C | Water |
Who will hear the sound first? Why?
Q 26.
If 20 waves are produced per second, what is the frequency in hertz?
Q 27.
What is the audible range of the average human ear ?
Q 28.
Distinguish between music and noise.
Q 29.
Deaf people can be made to dance to music.Explain how ?
Q 30.
What is speed of sound in air?
Q 31.
What are the factors speed of sound wave depends upon?
Q 32.
What is a wave number?
Q 33.
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 34.
Write differences between Transverse waves and Longitudinal waves.
Q 35.
What is reverberation?
Q 36.
Demonstrate an activity to show that sound requires a medium to travel.
Q 37.
Guess which sound has a higher pitch: guitar or car horn?
Q 38.
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 39.
Explain how sound is produced by your school bell ?
Q 40.
How can you show that sound waves are longitudinal waves ?
Q 41.
Try to imagine what you would feel, what sort of person you would be,had you been born totally deaf.
Q 42.
Fill in the blanks :
In a _____________ wave the particles of the medium oscillate in the direction in which the wave travels.
Q 43.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 44.
What is a longitudinal wave?
Q 45.
Suppose you and your friend are on the Moon. Will you be able to hear any sound produced by your friend?
Q 46.
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 47.
Explain the working and application of a sonar.
Q 48.
Can sound waves travel through vacuum ?
Q 49.
What is SONAR ? How is it used to detect an underwater object and measure its distance
Q 50.
Fill in the blanks :
Waves transport _________ not matter.
