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Homework Help: Two-slit interference

  1. May 3, 2009 #1

    1. The problem statement, all variables and given/known data

    A two-slit interference set-up with slit separation d =0.30 mm produces interference fringes at a particular set of angles THETAm (where m = 0, 1, 2,) for red light of frequency f = 4.9×10^14 hz.

    If one wishes to construct an analogous two-slit interference set-up that produces interference fringes at the same set of angles THETAm for room-temperature sound of middle-C frequency f = 262 hz, what should the slit separation distance be for this analogous set-up?
    this particular problems answer is 640 but i cant seem to arrive at that
    2. Relevant equations
    sin(theta)= m(wavelength)/d

    3. The attempt at a solution
    i believe sin(theta) is equalin both, so i dont see why it wouldnt come down to wavelenth/d is proprotional to wavelenth/d, or converting to frequency 1/fd = 1/fd or fd=fd.
    Last edited: May 3, 2009
  2. jcsd
  3. May 3, 2009 #2
    You know [tex]\lambda = v/f[/tex], but they both have different velocities so you can't use fd = fd.
  4. May 3, 2009 #3
    arent their velocities equal at c, being the speed of light?
  5. May 3, 2009 #4
    Sound doesn't travel at the speed of light. At least not where I live at.
  6. May 3, 2009 #5
    oh that is quite true, shouldnt have overlooked that, so i can now say the formula is
    c/fd = 343/fd?

    edit: yes i can, thanks alot nickjer, i got it now.
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