Facts that Matter
One complete back and forth motion of oscillating body about its mean (central) position is called a vibration or an oscillation.
For example, when we vibrate a tightly stretched metal string (Fig. 13.1), it makes a to and fro motion about its central position. During to and fro motions, string goes from upward extreme position to downward extreme position. When the string goes from upward extreme position to downward extreme position and then back to upward extreme position, we say that string has completed one vibration or one oscillation.
Frequency is equal to number of oscillations divided by time taken.
— The unit of frequency is hertz. It is denoted by Hz. If a vibrating body makes 20 oscillations in a second, we say that its frequency is 20 Hz.
The human voice can produce sounds with a frequency between 60 Hz and 13,000 Hz. It is interesting to note that a normal human ear can hear sound of frequency between 20 Hz to 20,000 Hz. The sounds of frequency higher than 20,000 Hz and less than 20 Hz cannot be heard by a human ear. The ears of some animals like bat, dog respond to sounds of frequency higher than 20,000 Hz. The sound of frequency greater than 20,000 Hz is called ultrasonic.
— Amplitude: During to and fro motion, a vibrating string goes a certain distance in the upward or downward direction from its central position, i.e. position of rest. The maximum distance to which the string goes upward or downward from its central position is called the amplitude.
The maximum displacement of an oscillating body from its central position is called amplitude.
The loudness is expressed in a unit called decibel (dB).