Sound is a form of energy. It causes the sensation of hearing. Sound is produced by vibrating bodies. When a particle (or body) moves to and fro about its mean position, it is said to vibrate. Every source of sound is a vibrating body. In the laboratory, a tuning fork is used to produce sound.
Production of sound
Sound is a mechanical wave and is normally associated with
our sense of hearing. Sound is produced by vibrating sources in a material
medium. The medium can be any gas, liquid or solid. A tuning fork, a violin string
and a loudspeaker are examples that produce sound.
This is because they are all in a state of vibration. The
energy of the sound waves is propagated and carried by colliding particles of a
material medium. Sound travels faster in denser media. It travels faster in
liquids than in gases and fastest in solids.
Sound cannot travel
through a vacuum
Sound is produced by a vibrating body. It is transmitted in the
form of mechanical waves. Thus, sound requires a material medium for its
propagation. Sound can travel through solids, liquids and gases.
Sound travels much
better in solids and at a very high speed as compared to liquids and gases. In the case of liquids, sound travels much better than in gases and at a higher speed.
From the above discussion, it can be understood that sound cannot travel
through a vacuum. It can be illustrated using the following experiment.
Experiment
Take an electric bell and fit an electric bell through an air-tight cork. Place the bell jar on the platform of the vacuum pump and supply a
little grease at its edges, to make it airtight.
Now press the key. It is possible to hear the sound of the
bell, as its hammer strikes against the gong. Now start the vacuum pump. It
will be observed that as the air is withdrawn from the bell jar, the loudness
of the sound of the bell decreases.
Furthermore, when a vacuum is created no sound is heard even though the hammer is striking against the gong. Stop the vacuum
pump and allow the air to enter a bell jar. The sound of the bell is heard
again.
This experiment proves that sound cannot travel through a vacuum and material medium is necessary for the propagation of sound.
Determining the speed
of sound in air
The speed of sound can be determined by direct method using
only two measurements.
The distance of the sound source from the receiver.
The time taken for the sound wave to travel that distance.
The speed of the sound can then be calculated using the
formula:
Speed = distance
travelled/time
Why is the thunder
heard after the flash of lightning?
Light travels with a speed of 3x108 m s-1,
whereas sound travels in air at 330 m s-1. Thus, whenever
lightning takes place, it can be seen first, whereas sound will take some to
reach us, depending upon the height of the cloud. This fact can be used for finding
the height of a cloud where lightning takes place.
Hold a stopwatch in your hand on a rainy day. As soon as you
see the flash of lightning, start the stopwatch. The moment you hear the sound
of thunder, stop the stopwatch.
Let us imagine that the time gap between seeing the lightning flash
and hearing the sound of thunder is T s. Knowing the velocity of sound in air
as 330 m s-1, we can find the height of the cloud as under,
Height of the cloud =
speed of sound in air x Time
Some common Terms used
in sound
Amplitude
The maximum displacement of a vibrating body from its mean
position is called amplitude. If a stationary body is struck slowly or with
less force, it has less amplitude. However, if the same body is struck hard, it has a large amplitude.
Frequency
The number of vibrations produced by a vibrating body in one
second is called frequency.
Units of frequency
The unit of frequency in the SI system is hertz (Symbol Hz). When
a vibrating body produces one vibration in one second, then its frequency is
said to be one hertz. If the frequency of a tuning fork is 256 Hz, it means it
is producing 256 vibrations in one second.
Bigger Units of
Frequency
Bigger units of frequency are kilohertz (symbol kHz) and
megahertz (MHz).
1 kHz = 1000 Hz
1 MHz = 1000,000 Hz
Time period
The time in which a vibrating body completes one vibration is
called a period. It is denoted by the letter T.
Do all vibrations
produce Sound?
The human ear is not sensitive to vibrations of all frequencies.
If the frequency of the vibrations is less than 20 Hz, then the human ear cannot
perceive them. Such vibrations are called subsonic vibrations or infrasonic
vibrations.
If the frequency of vibrations is between 20 Hz to 20,000 Hz,
then they can be perceived by the human ear. Such vibrations are called sonic
vibrations or sound vibrations. It has been further found that the higher the
frequency, the sharper or shriller the effect of sound on the ears.
However, if the frequency of vibrations is above, 20,000 Hz,
then they can be perceived by the human ear. However, if the frequency of
vibrations is above 20,000 Hz, then the human ear cannot perceive them. Such
vibrations are called ultrasonic vibrations or ultrasonic.
Application of
Ultrasonic sounds
These are used for the treatment of inoperable brain tumours.
It is used to detect flaws and blowholes in metal casting.
In the welding together of two pieces of metals, the heat
produced by friction between the metals due to the vibrations of one of them at
ultrasonic frequency fuses them and welds them together.
It is used to kill bacteria in milk.
Ultrasonic sound is used to control smoke and clear fog.
Special whistles using ultrasonic waves which are inaudible to the human ear are used to call dogs.
Reviewed by knowledge people creators
on
December 20, 2021
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