Doppler effect
The Doppler effect is a change in frequency and wavelength of a wave. It is caused by the change in distance between the thing creating the wave (causer) and whatever is measuring seeing or hearing the wave (watcher or observer).[1]
Another word for "causer" is "sender" or "source". Another word for "change in distance" is "speed" or "relative velocity". A common example is sitting in a car while another car goes by the watcher. The watcher will hear a change in pitch, while the sender will not.
For waves read all the waves that can send out or reflected by an object. And for reflection read change of direction of a wave.
Effects of changes in distance
If observer and creator of the wave get closer, the frequency is higher and the wavelength is shorter.
- For light, this causes a shift in colour towards the blue end of the spectrum called a blue shift. The faster something is moving toward us, the greater the blue shift.
- For sound, this causes the sound to become higher in pitch
If the distance between the observer and creator gets longer, the frequency is lower and the wavelength is longer.
- For light, this causes a shift towards the red end of the spectrum called a red shift, the faster something is moving away, the greater the red shift.
- For sound, this causes the sound to become lower in pitch.
Light waves can also be read, examples are:
An extreme example of the doppler effect is an aeroplane flying at a faster speed than the speed of sound and how the wall of sound is heard on the ground.
Doppler Effect Media
Change of wavelength caused by motion of the source.
Sirens on passing emergency vehicles.
Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to that of the Sun (left)
U.S. Military Police using a radar gun, an application of Doppler radar, to catch speeding violators.
Colour flow ultrasonography (Doppler) of a carotid artery – scanner and screen
Possible Doppler shifts in dependence of the elevation angle (LEO: orbit altitude h = 750 km). Fixed ground station.
Geometry for Doppler effects. Variables: \vec{v}_\text{mob} is the velocity of the mobile station, \vec{v}_\text{Sat} is the velocity of the satellite, \vec{v}_\text{rel,sat} is the relative velocity of the satellite, \phi is the elevation angle of the satellite and \theta is the driving direction with respect to the satellite.
Doppler effect on the mobile channel. Variables: f_c = \frac{c}{\lambda_{\rm c}} is the carrier frequency, f_{\rm D,max}=\frac{v_{\rm mob}}{\lambda_{\rm c}} is the maximum Doppler shift due to the mobile station moving (see Doppler Spread) and f_{\rm D,Sat} is the additional Doppler shift due to the satellite moving.
Related pages
References
- ↑ Wragg, David W. (1973). A Dictionary of Aviation (first ed.). Osprey. p. 112. ISBN 9780850451634.