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11. Sound eLearn.Punjab

11.7 AUDIBLE FREQUENCY RANGE

For your information We know that sound is produced by a vibrating body. A normal
human ear can hear a sound only if its frequency lies between 20Hz

and 20,000 Hz.

In other words, a human ear neither hears a sound of frequency less

than 20 Hz nor a sound of frequency more than 20,000 Hz. Different

people have different range of audibility. It also decreases with age.

Young children can hear sounds of

20, 000 Hz but old people cannot Tidbits
Pilots wear special headphones hear sound even above 15,000 Hz.
Bats can hear frequencies up to
that reduce the roar of an airplane 120,000 Hz. Other animals cannot
engine to a quiet hum. hear such high-pitched sounds.
Mice can hear frequencies up to
The range of the frequencies which a human ear 100,000 Hz, dogs up to 35,000 Hz,
can hear is called the audible frequency range. and cats up to 25,000 Hz. Humans
hear sounds only upto about
20,000 Hz, but children can usually
hear higher-frequency sounds
than adults.

11.8 ULTRASOUND

Sounds of frequency higher than 20, 000 Hz which are inaudible to
normal human ear are called ultrasound or ultrasonics.

Uses of Ultrasound
• Ultrasonic waves carry more energy and higher frequency than audible sound waves. Therefore,

according to the wave equation v=fλ, the wavelength of ultrasonic waves is very small and is very
useful for detecting very small objects.
• Ultrasonic are utilized in medical and technical fields.

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