Question:
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?
Answer:
Person A will hear the sound first because sound travels the faster in solids than in liquids and gases.
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.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is
440 m/s in a given medium.
Q 12.
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 13.
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 14.
Fill in the blanks :
Number of oscillations completed by the oscillator in one second is known as ___________.
Q 15.
Fill in the blanks :
v = ? × ?
Q 16.
What is speed of sound in air?
Q 17.
Demonstrate an activity to show that sound requires a medium to travel.
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.
What is audible range ?
Q 21.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 22.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 23.
What is Sound? Why it is important for us?
Q 24.
What is a mechanical wave?
Q 25.
If 20 waves are produced per second, what is the frequency in hertz?
Q 26.
What type of wave is represented by density- distance graph?
Q 27.
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 28.
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 29.
What is the audible range of the average human ear ?
Q 30.
Distinguish between music and noise.
Q 31.
What is SONAR ? How is it used to detect an underwater object and measure its distance
Q 32.
Try to imagine what you would feel, what sort of person you would be,had you been born totally deaf.
Q 33.
Suppose you and your friend are on the Moon. Will you be able to hear any sound produced by your friend?
Q 34.
What are the factors speed of sound wave depends upon?
Q 35.
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 36.
A bat emits ultrasonic sound of frequency 100 kHz in air.If this sound meets a water surface,what is the wavelength of (a) the reflected sound wave (b) the transmitted sound wave ?
Given speed of sound in air = 340 m/s and in water = 1486 m/s.
Q 37.
Can sound waves travel through vacuum ?
Q 38.
Deaf people can be made to dance to music.Explain how ?
Q 39.
Fill in the blanks :
Waves transport _________ not matter.
Q 40.
Fill in the blanks :
In a _____________ wave the particles of the medium oscillate in the direction in which the wave travels.
Q 41.
What is a longitudinal wave?
Q 42.
How does the sound produced by a vibrating object in a medium reach your ear?
Q 43.
What is a wave number?
Q 44.
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 45.
What is reverberation?
Q 46.
Which wave characteristics determine the
(a) Loudness (b) pitch of sound?
Draw two different waveforms and mark these characteristics on it.
Q 47.
Guess which sound has a higher pitch: guitar or car horn?
Q 48.
Calculate the wavelength of a sound wave having a frequency 300 Hz and speed 330 m/s.
Q 49.
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 50.
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.
