1. Doppler Effect

2. Moving Source  Light moves equally in all directions from a source. Circular (or spherical) patternCircular (or spherical) pattern  If the source is moving the origin of successive circles moves.

3. Wavelength Shift  The normal period is T and the observer moves at speed u.  The wavelength ahead of the source is shorter. ’  = - uT  The wavelength behind the source is longer. ’  = + uT

4. Frequency Shift  The period is related to the wavelength.  This can be converted into a frequency shift. Requires correction for special relativityRequires correction for special relativity

5. Moving Observer  If the observer is moving toward the source the effect is similar, but the wave crests have a different relative spacing. A speed gun uses a double Doppler shift. There is a shift for both the pulse out and reflected signal.

6. Speed Gun  A speed gun used the doppler shift twice. Shift for pulse out and pulse backShift for pulse out and pulse back