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Homework Help: Photon Emission Rate and Optics Questions

  1. Apr 4, 2005 #1
    I'm really lost on these 3 questions. My physics teacher decided she was sick of thermodynamics and gave us this packet over material we haven't covered yet, but she expects us to get it without any problem. I'm really stuck on these:

    1. Assume that sodium produces monochromatic light with a wavelength of 5.89x10^-7 m. At what rate would a 10 watt sodium vapor light be emitting photons?
    A. 3.5x10^19 photons/s
    B. 3.0x10^19 photons/s
    C. 2.5x10^19 photons/s
    D. 2.0x10^19 photons/s
    I don't even know how to start this problem. We have never done anything with photons yet in our class. I tried looking for an equation, but I couldn't find anything. Does anybody know a certain equation I have to use to solve this?

    2. Non-polarized light first passes through one polarizing filter and then through a second. If the intensity of light emerging from the second filter is 12.5% of hte light that struck the first filter, at what angle must the axes of the two filters be with respect to one another?
    A. 7 degrees
    B. 30 degrees
    C. 42 degrees
    D. 60 degrees
    E. 83 degrees
    Again, we have never covered polarization, but I think to find an angle you have to use inverse tangent. I just don't know what value to use the inverse tangent on. How can I solve this problem??

    3. At transmission, diffraction grating is ruled with 5000 lines per cm. Through what angle will the first order maxima be deflected when light with a wavelength of 4.5x10^-7 m strikes the grating at an angle of incidence of 0 degrees?
    Again, never had this material. But again, don't you use the inverse of a function to find the angle needed? But like in the last problem, I don't know what value to use the inverse on. Is there a formula I could use?

    All help is appreciated. Thanks.
  2. jcsd
  3. Apr 4, 2005 #2


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    It's not okay (for me,at least,if i were you,even if just for a sec) to think of solving problems without knowing the theory first.So how about either wait till u cover the theory in class,or do some reading from the textbook...?

  4. Apr 4, 2005 #3
    I'm reading. I was able to solve the other 5 problems that came with these. But, these questions are due tomorrow at the beginning of class... Which means, we're not going over them.
  5. Apr 4, 2005 #4
    Oh, and our textbook is a Conceptual PHysics book, and there is no math in it. so I can't really consult it. This isn't the first time I've received random problems I didn't know how to do.
  6. Apr 4, 2005 #5


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    You don't need math.These problems are all about logics (<--------Conceptual Physics) and simple arithmetics & algebra...

    I'll let someone else do the theory explanation.

  7. Oct 16, 2011 #6
    the ans is the 2nd option.

    the original answer is 2.971*10^19.
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