# (a) What are infrasonic waves? Name two animals which produce infrasonic waves.(b) What are ultrasonic waves? Name two animals which can produce ultrasonic waves(c) The audible range of frequencies of an average human ear is from 20 Hz to 20 kHz. Calculate the corresponding wavelengths. (Speed of sound in air is $344\ ms^{-1}$).

(a). Sounds of frequencies below $20\ Hz$ are known as Infrasonic waves.

These sounds are produced by objects vibrating very slowly.

Whales and elephants are two living creatures who can produce these Infrasonic sounds.

(b). Sounds of frequencies above 20,000 Hz are known as Ultrasonic waves.

These sounds are produced by objects vibrating very rapidly.

Bats and dolphins can produce these sounds.

(c). Speed of sound $v=344\ m/s$
Lower frequency $f_l=20\ Hz$
Higher frequency $f_h=20,000\ Hz$

Wavelength with lower frequency $\lambda_l=\frac{spees}{frequency}$

$=\frac{344\ m/s}{20}$

$=17.2\ m$

So, the wavelength$(\lambda_l)$ corresponding to lower frequency is $17.2\ m$.

Wavelength corresponding to high frequency $\lambda_h=\frac{speed(v)}{frequency(f_h)}$

$=\frac{344\ m/s}{20000\ Hz}$

$=0.01732\ m$

$=1.732\ cm$

Therefore, wavelength corresponding to high frequency is $1.732\ cm$.

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Updated on: 10-Oct-2022

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