Sound Worksheet

Sound

Points to remember:

1.       Sound is the mechanical energy that can be detected with our ears.

2.       Sound is produced by vibrating objects.

3.       During the propagation of sound, particles of the medium only vibrate and do not actually move from the vibrating body to the listener.

4.       A material medium is essential for the propagation of sound waves, and hence it cannot travel in vacuum.

5.       Thus, sound can be defined as a form of energy which is emitted by a vibrating source and transmitted through a material medium producing in us the sensation of hearing.

6.       Sound waves are longitudinal waves. It propagates as a series of compressions (increased density or pressure) and rarefactions (decreased density or pressure).

7.       In longitudinal waves, the particles of the medium vibrate along the direction of propagation of the wave. In transverse waves, the particles of the medium vibrate in a direction perpendicular to the direction of propagation of the wave. Light is an example of transverse waves.

8.       In a sound wave,

a.       A compression is represented by a peak (or crest) and a

rarefaction by a valley (or trough).

b.      The change in density in the medium from maximum value to

minimum value and again to the maximum value is one oscillation.

c.       Amplitude (A) is the magnitude of the maximum disturbance in the

medium due to the disturbance.

d.      Frequency (ʋ, Greek letter, nu) of the wave is the number of complete oscillations in density of the medium per second. Unit is Hz (hertz).

e.      Time period (T) of the wave is the time taken for one complete oscillation in density of the medium. Unit is s (second).

f.        Wavelength (ƛ, Greek letter, lamda) is the distance travelled by a wave in a unit time period. Unit is m (metre). It can also be defined as the distance between two consecutive compressions or rarefactions.

g.       Speed of sound (v) is the distance travelled by the sound wave per unit time. Unit is m/s.

h.      <i=<r and ʋ=v ƛ (** to solve problems: Write the given data in terms of T, ʋ, ƛ or v and apply any of the two formulae as and where required.)

9.       Speed of sound in solids> Speed of sound in liquids> Speed of sound in gases (*may not always be valid)

10.   Speed of sound is much lesser than the speed of light.

11.   Speed of sound increases with increase in temperature.

12.    Sounds have 2 main characteristics:

a.       Loudness (dependent on the amplitude)

b.      Pitch or shrillness (frequency)

13.   Sound of a single frequency is called a tone; several frequencies mixed together are called a note.

14.   Music consists of series of regular sound impulses and has a pleasant effect on the ear. The frequency is high, but there are no sudden changes in the amplitude of the sound.

15.   Noise consists of irregular sound impulses and has an unpleasant effect on the ear. The frequency is low, and there are sudden changes in the amplitude of the sound.

16.   Laws of reflection of sound:

a.       ˪r=˪i  (angle of reflection shall always be equal to angle of incidence of the sound wave)

b.      The incident wave, the reflected wave and the normal at the point of incidence, all lie in the same plane.

17.   Echo is the repetition of sound due to its reflection from an obstacle.

18.   The sensation of sound lasts in our brain for 0.1s. so, to hear an echo, the sound must return after 0.1s.

19.    Minimum distance required to hear a distinct echo is approximately 17m.

20.   Echoes are made use of in applications like speaking tubes, hearing aids, stethoscope, designing of concert and cinema halls, etc.

    

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