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There are three important properties of sound
- Amplitude
- Frequency
- Time Period
What is Amplitude
It is maximum displacement of a vibrating object from its central location
Explanation
We know that sound is produced due to vibration of particles(To and Fro Motion)
We know that in to and fro motion,an object moves from its central position
More it moves from its central position, more is the amplitude
Less it moves from its central position, less is the amplitude
Note - More Amplitude means More Loudness of Sound
Loudness is directly proportional to the square of Amplitude
If amplitude becomes double, loudness becomes 4 times
If amplitude becomes half,loudness becomes ¼ times
The loudness is expressed in a unit called decibel (dB).
Note
Roaring of lion can be heard over long distances because it has higher amplitude
Frequency of Sound
Number of vibrations made in one second is called frequency of sound
It is measured in Hertz
Explanation
We know that sound is produced due to vibration of particles(To and Fro Motion)
More times it moves in one second,more is the frequency
Less times it moves in one second,less is frequency
Example 1
Suppose if vibration of sound is 50 vibrations per second,
it means its frequency is 50 hz
Note - Frequency determines shrillness or pitch of sound
More the frequency, more the shrillness of sound
Less the frequency, less the shrillness of sound
Example 1
Voice of Baby is of high pitch
Voice of grown up man is low pitch
Example 2
Chirping of Bird is of high pitch
Roaring of lion is of low pitch
Time Period of Sound
The time taken by the wave to one complete oscillation is called the time period
It is measured in seconds
Relationship between Time Period and Frequency
Time Period = 1/Frequency
Example
Suppose Frequency of an object is 20 Hertz
It means that it makes 20 vibrations in 1 second
Time taken for 1 vibration=1/20=0.05 seconds
Questions
NCERT Question 2 - Which of the following voices is likely to have minimum frequency?
Baby girl (b) Baby boy (c) A man (d) A woman
NCERT Question 3 (b) - Mark True or False
The number of oscillations per second of a vibrating object is called its time period. (T/F)
NCERT Question 3 (c) - Mark True or False
If the amplitude of vibration is large, sound is feeble. (T/F)
NCERT Question 3 (e) - Mark True or False
If the amplitude of vibration is large, sound is feeble. (T/F)
NCERT Question 4 (a) - Fill in the blanks with suitable words.
Time taken by an object to complete one oscillation is called...................
NCERT Question 4 (b) - Fill in the blanks with suitable words.
Loudness is determined by the .........................of vibration.
NCERT Question 4 (c) - Fill in the blanks with suitable words.
The unit of frequency is..........................
NCERT Question 4 (e) - Fill in the blanks with suitable words.
Shrillness of a sound is determined by the ................. of vibration.
