8/12/2019 Sound -9

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JOHNSON FOUNDATION SCHOOL

Class 9 Physics Assignment in Sound ! "# ! $""9

1) Sound is a longitudinal wave that is created by a vibrating object, such as a guitar string, the human vocal

cords, or the diaphragm of a loudspeaker.

2) Sound is a form of energy which excites in our ears the sensation of hearing.

) Sound cannot exist in a vacuum.!) Sound is produced by a vibrating body. "ut not all vibrating bodies produce sound which we can hear.

#hese whistles are called $alton whistle.%) &aves which re'uire medium for their propagation are called mechanical waves. #hese waves transmitenergy and momentum, not the matter.

() #he waves are of two types, mechanical waves and electromagnetic waves.

) #he mechanical waves transport energy from one place to another in a medium.*) +aterial medium is re'uired for the transport of energy for the mechanical waves. #he medium should be

elastic and should possess inertia.

) -n mechanical waves, the energy and momentum are transported by means of a disturbance in the medium.#his disturbance will be propagated because the medium has elastic properties.

1) -n electromagnetic waves, the energy and momentum are carried by electric and magnetic fields.

11) -n sound waves, a disturbance in the pressure and density of air is set up by the vibration of body and the

disturbance is propagated through the air by the collision of air molecules.12) #he water particles on the surface of water waves move in nearly circular paths having both longitudinal

and transverse components.

1) #he sounds of fre'uency less than 2/0 are called infrasonics. #he sound of fre'uency greater than2/0 are called ultrasonics.

1!) ltrasonic waves can be produced by magnetostriction oscillator and pie0o electric oscillator.

1%) #here are two types of wave namely transverse and longitudinal.1() -f particles of the medium vibrate perpendicular to the direction of propagation of the wave, then the wave

is said to be transverse.

1) crest and a trough make up a complete transverse wave.

1*) -f the particles of the medium vibrate parallel to the direction of propagation of the wave, then the wave is

said to be longitudinal.1) compression and a rarefaction make up a complete longitudinal wave.

2) the distance traveled by the wave in the time the particle of the medium completes one oscillation is known

as wavelength 3)

21) #he distance traveled by the wave in one second is known as wave velocity or phase velocity.

22) 4hase is that which gives the state of the vibrating particle as regards its position and direction of the

motion. 5re'uency is an objective property of a sound wave, because fre'uency can be measured with an

electronic fre'uency counters.2) #he speed of sound is a medium depends upon i) 6lasticity of the medium and

ii) 7ensity of the medium 8 9E

p

2!) #he e'uation for the velocity of sound in air is v 9rp

d

2%) Sound travels more than ! times faster in water and more than times faster in steel than it does in air.2() -n air sound travels 2 ms:1at 2;.

2) 8elocity of sound in air is independent of pressure of air.

2*) 8elocity of sound varies inversely as the s'uare root of density.2) 5or every degree ;elcius change in temperature the velocity of sound changes by .(1 ms:1.

) 8elocity of light is very large as compared to velocity of sound.

Nume%icals

1) #he fre'uency of a tuning fork is % /0. ;alculate the time period.2) n electric tuning fork completes one oscillation in .12% s. ;alculate the fre'uency of tuning fork. &ill

the sound emitted by tuning fork be audiablemin. ;alculate 3i) time period 3ii) wave length.

) i ) #he diagram alongside shows a displacement distance graph

of a wave. -f the velocity of wave is 1( ms :1,calculate 3i) wave length ii) fre'uency iii) amplitude

ii) 5rom the diagram alongside calculate

3i) velocity of 4 and ? 3ii) fre'uency of 4.&hen fre'uency of ? is %12 /0.

ssume both wave are traveling in same medium.