Can someone explain what's a Doppler's effect?
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ANSWERS: 2
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Waves can only move so fast. How fast they move depends on the type of wave and the medium through which the move. For any given set of conditions, the waves will move at a constant speed. Given this, if either the wave source or observer is moving with respect to the other, then the observer will perceive the wavelength of the waves changing depending on their respective positions. If the wave source is approaching the observer, then he will perceive the wavelength as being compress. If the source in moving away, then he will perceive the wavelength as being stretched out. This change in wavelength with result in a change in pitch in the case of sound waves and a change in color in the case of light. For more, see http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/waves/u10l3d.html
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Waves always travel at a set speed. Sound travels at the local speed of sound in the medium and electromagnetic waves travel at the local speed of light. For the electromagnetic spectrum (which contains light) if you were to look at a stationary bulb far away, you would be seeing photons (light waves basically) coming away from it at a set frequency. The gap between the emission of these photons is the wave length. Now if you move the bulb closer to you, the gap between these photons decreases (and hence the wavelength) this is because the last photon will have move towards you a set distance, but the bulb will have moved forward too eating up this distance when the next photon is emitted. Since these photons all travel at the same speed the gap is maintained. This decrease in wavelength shifts the light you see from the bulb towards the blue end of the spectrum and is called "blue-shifted". If the bulb moves away similarly the gap increases. This shifts the light you see towards the red end of the spectrum.
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