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Amplitude, Time Period, Frequency

Amplitude of the sound is nothing but the loudness or the amount of maximum displacement of the particles while the sound is produced.



When the amplitude of the vibration is large, the sound produced is loud. When the amplitude is small, the sound is feeble.


Frequency of Sound
The number of oscillations per second is called the frequency of the oscillation. Frequency is expressed in terms of hertz.


Loudness and Pitch

Loudness depends on the amplitude of vibrations. Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. If the amplitude becomes twice, the loudness increases by a factor of 4. The loudness is expressed in a unit called decibel (dB).


The following table gives some idea of the loudness of sound coming from various sources.


Normal breathing

10 dB

Soft whisper
30 dB
Normal conversation
60 dB
Busy traffic
70 dB
Averarge traffic
80 dB

Above 80 dB, the noise becomes physically painful.

Compare the sound of yours and your teacher’s. Is there any difference? Even if the two sounds are equally loud, they differ in some way. The difference in sound is due to the shrillness or pitch of the sound. If the sound has high frequency, then it has high pitch or shrillness. If the frequency of vibration is low, then it has low pitch e.g. vibration of drums.



Audible Sounds
Sounds which we can hear is about 20 Hz to 20,000 Hz. These sounds are called audible sounds.

Inaudible Sounds

Ultrasonic Sounds: These squirrels communicate with each other with a frequency greater than 20,000Hz. These sounds are called as ultrasonic. Dogs and Whales have the ability to hear ultrasonic sounds.

Did you know?

The ultrasonics are used to take the scan pictures of various vital organs.

Infrasonic Sounds: Sounds which have frequency less than 20 Hz are termed as infrasonics.

The Squirrel's Secret: Ultrasonic Warning Calls



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