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What is Range of Hearing of Human Beings
It is 20 Hz to 20000 Hz
However, children under age of 5 can hear upto 25000 Hz
Difference between Audible and Inaudible Sounds
| Audible Sounds |
Inaudible Sounds
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| Sounds which can be heard by us are called Audible Sounds |
Sounds which we are not able to hear are called Inaudible Sounds
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Range of Audible Frequency for Human ear is 20 Hz to 20000 Hz
It means human beings can hear sound having frequency from 20 Hz to 20000 Hz |
Human beings cannot hear
Sound having frequency less than 20 Hz (Called Infrasonic or Infrasound) Or Having Frequency more than 20000 Hz (Called Ultrasonic or Ultrasounds) |
What are Infrasonic Sounds
Sounds having frequency less than 20 Hz are called Infrasonic Sounds
Note
Human beings cannot hear infrasonic sounds
However some animals can communicate using infrasonic sound
Example-
Rhinoceros, whales and Elephants
Why do some animals get disturbed before earthquakes
Because earthquake produce low frequency sounds before main earthquake begins
These low frequency sounds alert these animals
What are Ultrasonic Sounds or Ultrasounds?
Frequency higher than 20000 Hz (20 kHz) are called Ultrasonic Sounds
it is produced by certain animals like Moths, bats, rats
Some animals such as dogs, bats and dolphins can hear ultrasounds
How does Bats use Ultrasound
Bats use ultrasound to navigate (move) and catch prey
Procedure
- Bats produce high frequency ultrasonic squeaks
- These squeaks reflect on prey and return back to bats ear
- This gives bats idea of location of prey
- Similarly,to find direction,bats use squeaks to find obstacles
- These squeaks reflect on obstacle and return to bats ear
- This helps bats to navigate (move)
How are moths able to escape attack of bats?
Some Moths have very sensitive ears
They are able to hear high frequency squeaks of bats
When they hear such squeaks
They change direction and are able to escape attack of bats
Questions
Question 1 Page 170 - What is the audible range of the average human ear?
Question 2 Page 170 -
"What is the range of frequencies associated with (a) Infrasound? (b) Ultrasound?"
NCERT Question 14 - A sound wave travels at a speed of 339 m s–1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
NCERT Question 17 - Explain how bats use ultrasound to catch a prey.
