Physical Semestral Guide 2/many

​Infrasonic Waves (Infrasound)

Infrasonic waves have frequencies below 20 Hz, which makes them inaudible to the human ear. Scientists use infrasound to detect earthquakes and volcanic eruptions, to map rock and petroleum formations underground, and to study activity in the human heart.

​Ultrasonic Waves (Ultrasound)

Sound waves that have frequencies higher than 20,000 Hz produce ultrasound. Because ultrasound occurs at frequencies outside the human hearing range, it is inaudible to the human ear. Ultrasound is most often used by medical specialists who use sonograms to examine their patients’ internal organs.

​Relation between frequency and period

f = Frequency

T = Period 

​The frequency is measured in Hertz (Hz), the Wavelength is measured in meters (m) and Period is measured in seconds (s).

If the relative velocity of observer and source are towards each other the frequency will be higher than the original frequency.  If the relative velocity of observer and source are away from each other the frequency will be lower than the original frequency.

​Where:

f = frequency perceived

f_o = original frequency from the source

v = velocity of sound

v_o = velocity of the observer (+ if going towards the source and - if going away from the source)

v_s = velocity of the source (- if going towards the source and + if going away from the source)