Re: what is the velocity of ultrasonics in air?on what factors does it depend ?

Hi Ganesa,

In air, the speed of sound (including ultrasound) depends mostly on temperature. The equation that describes the dependence of sound speed (c, in m/s) on air temperature (T, in degrees Celsius) is:

c = 331.5 + 0.6 * T

This is an approximation that works for most of the range of temperatures and humidities we experience on the surface of the earth. See the Wikipedia article on the speed of sound for a more complete description of what sound speed depends on.

As for the relationship between sound speed (or velocity) and its frequency (f, in Hz),

c = WL * f,

where WL is the wavelength of the sound (in m). Since the sound speed is fixed for given atmospheric conditions, the wavelengths at ultrasonic frequencies (defined as sonic frequencies higher than human hearing, i.e. greater than about 20 kHz) are quite short compared to those in music, for example.

I hope this helps.
Cheers,
Tetjana