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Homework Help: Beat frequency

  1. Nov 8, 2005 #1
    There are two parts to this but i solved the first part:
    in part a) i was to show, for an electomagnetic wave reflected back to its source from a mirror approaching at speed v, that the reflected wave had frequency [tex] f=f_{source}\frac{c+v}{c-v}[/tex] where fsource is the source frequency and c is the speed of light.

    now i am asked: when v is much less than c, the beat frequency is much smaller than the transmitted frequency. In this case use the approximation [tex] f + f_{source}\approx 2f_{source}[/tex] and show that the beat frequency can be written:

    [tex]f_{beat}=\frac{2v}{\lambda}[/tex]

    i dont know how to go about this. I was thinking to solve for fsource and put it into the equation from part a. but this doesnt work...any help
     
  2. jcsd
  3. Nov 9, 2005 #2
    no help on this...........
     
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