Answer:
Wavefronts are the surfaces over which the vibrations due to sound wave have same value. For near sound source, wavefronts are considered spherical while for the distance source of sound the wavefronts are considered planar.
Sound
Q 1.
Why do we use upholstered seats in theatres and halls ?
Q 2.
What are the factors speed of sound wave depends upon?
Q 3.
Fill in the blanks :
v = ? × ?
Q 4.
What are ultrasonics?
Q 5.
What propagates along with the waves ?
Q 6.
Obtain a relation between speed,frequency and wavelength of a wave.
Q 7.
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 8.
Explain how sound is produced by your school bell ?
Q 9.
Explain how the human ear works.
Q 10.
How is sound propagated through a material medium ? What is wave motion ?
Q 11.
What is a wave number?
Q 12.
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 13.
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 14.
Fill in the blanks :
The product of wavelength of wave and its frequency gives _____________.
Q 15.
How does sound travel in gases and liquids as longitudinal or as transverse waves?
Q 16.
What are wavefronts?
Q 17.
What is infrasonic? Give an example.
Q 18.
A boat anchor is rocked by waves whose consecutive crests are 100 m apart.If the wave speed of the moving crests is 20 m/s,calculate the frequency at which the boat rocks.
Q 19.
Calculate the wavelength of a sound wave having a frequency 300 Hz and speed 330 m/s.
Q 20.
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 21.
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 22.
What is the audible range of the average human ear ?
Q 23.
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 24.
What are wavelength, frequency, time period and amplitude of a sound wave?
Q 25.
What type of wave is represented by density- distance graph?
Q 26.
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 27.
What is audible range ?
Q 28.
Guess which has a higher pitch : a guitar or a car horn ?
Q 29.
Explain the working and application of a sonar.
Q 30.
Try to imagine what you would feel, what sort of person you would be,had you been born totally deaf.
Q 31.
What travels faster : a rifle bullet or the sound of the shot fired from it ?
Q 32.
Fill in the blanks :
If a body repeats its motion, within fix interval of time, along a certain path, about a fixed point, it is said to have ____________.
Q 33.
If 20 waves are produced per second, what is the frequency in hertz?
Q 34.
The sonic boom of an aircraft has a time period of 0 00005 s.Calculate the frequency of the sound produced.
Q 35.
What are wavelength,frequency,time period and amplitude of a sound wave ?
Q 36.
How are the wavelength and frequency of a sound wave related to its speed ?
Q 37.
What is reverberation ? How can it be reduced ?
Q 38.
When you shout in front of a hill,your own shout is repeated.Explain.
Q 39.
Write the name of the wave which propagates in terms of compressions and rarefactions.
Q 40.
What is the minimum distance of the obstacle from the source of sound for hearing distinct echo ?
Q 41.
What do you mean by reverberation and reverberation time ? How is reverberation controlled ?
Q 42.
Deaf people can be made to dance to music.Explain how ?
Q 43.
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 44.
Can sound wave travel in vacuum?
Q 45.
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 46.
Give an application use of ultrasonics.
Q 47.
Distinguish between loudness and intensity of sound.
Q 48.
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 49.
Does sound follow the same laws of reflection as light does ? Explain.
Q 50.
Explain how defects in a metal block can be detected using ultrasound.
