Question:
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.
Answer:
(a) 340 m/s (b)1870 m
Sound
Q 1.
What are ultrasonics?
Q 2.
What are the factors speed of sound wave depends upon?
Q 3.
What is a wave number?
Q 4.
How is sound propagated through a material medium ? What is wave motion ?
Q 5.
How are compressions and rarefactions produced near a source of sound ?
Q 6.
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.
Q 7.
Fill in the blanks :
v = ? × ?
Q 8.
What type of waves can travel in vacuum? Give example(s).
Q 9.
Explain how sound is produced by your school bell ?
Q 10.
Sounds we hear inform us of the state of world around us,especially of that part of it which our other senses,such as touch and sight,cannot reach.Illustrate this with appropriate examples.
Q 11.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 12.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 13.
What is infrasonic? Give an example.
Q 14.
What is audible range ?
Q 16.
Fill in the blanks :
Waves transport _________ not matter.
Q 17.
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 18.
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 19.
What propagates along with the waves ?
Q 20.
Why do we use upholstered seats in theatres and halls ?
Q 21.
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 22.
How are the wavelength and frequency of a sound wave related to its speed?
Q 23.
What type of wave is represented by density- distance graph?
Q 24.
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 25.
Deaf people can be made to dance to music.Explain how ?
Q 26.
What is a mechanical wave?
Q 27.
What is speed of sound in air?
Q 28.
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 29.
Give an application use of ultrasonics.
Q 30.
Guess which sound has a higher pitch: guitar or car horn?
Q 31.
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 32.
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 33.
How are the wavelength and frequency of a sound wave related to its speed ?
Q 34.
Explain the working and application of a sonar.
Q 35.
What is sonic boom and when is it heard ?
Q 36.
Fill in the blanks :
Sound, compressional waves in springs are examples of _____________.
Q 37.
What are wavelength, frequency, time period and amplitude of a sound wave?
Q 38.
What is reverberation?
Q 39.
Distinguish between loudness and intensity of sound.
Q 40.
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 41.
What is the audible range of the average human ear ?
Q 42.
How can you show that sound waves are longitudinal waves ?
Q 43.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 44.
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 45.
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 46.
What is Sound? Why it is important for us?
Q 47.
What are wavefronts?
Q 48.
How does the sound produced by a vibrating object in a medium reach your ear?
Q 49.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 50.
If 20 waves are produced per second, what is the frequency in hertz?
