The+Doppler+effect

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**Doppler effect**
Describe what is meant by the Doppler effect. The **Doppler effect** (or **Doppler shift**) is the change in frequency of a wave for an observer moving relative to the source of the wave. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession. If the rod had been vibrating in one place, we would have seen the familiar pattern of concentric circles, all centered on the same point. But since the source of the waves is moving, the wavelength is shortened on one side and lengthened on the other. The pattern of waves made by a point source moving to the right across the water. Note the shorter wavelength of the forward-emitted waves and the longer wavelength of the backward-going ones.

The velocity is constant, the equation //v//=//f//λ; The change in wavelength must be matched by an opposite change in frequency: higher frequency for the waves emitted forward, and lower for the ones emitted backward.

The frequency Doppler effect is the reason for the familiar dropping-pitch sound of a race car going by. As the car approaches us, we hear a higher pitch, but after it passes us we hear a frequency that is lower than normal.

Hubble discovered that except for a few very nearby ones, all the galaxies had red shifts, indicating that they were receding from us at a hefty fraction of the speed of light. Not only that, but the ones farther away were receding more quickly. The speeds were directly proportional to their distance from us.

= = VIEW THE DOPPLER EFFECT: Simulation - DOPPLER APPLET Physics 2000 - [|The Doppler Effect 1] Physics 2000 - [|The Doppler Effect 2] Walter Fendt - [|The Doppler Effect]

Explain the Doppler effect by reference to wavefront diagrams for moving-detector and moving-source situations.

Apply the Doppler effect equations for sound. Solve problems on the Doppler effect for sound.

Problems will not include situations where both source and detector are moving. Solve problems on the Doppler effect for electromagnetic waves using the approximation

Δf = (v/c)f Δf = the changes in frequency v = the relative speed of the source and observer c = the speed of light in a vacuum fo = the original frequency Students should appreciate that the approximation may be used only when v << c.

This can also be written as Δλ=vλ/c
 * [[image:nothingnerdy/dopplerstar.gif width="377" height="300" caption="dopplerstar.gif"]] || [[image:doppler-1.jpg width="385" height="301"]] ||

Outline an example in which the Doppler effect is used to measure speed Suitable examples include blood-flow measurements and the measurement of vehicle speeds. = Wave phenomena =