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Homework Help: LASER Problems HELP NEEDED!

  1. May 19, 2010 #1
    LASER Problems!! HELP NEEDED!

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

    1. The carbon dioxide laser usually emits at 10.6 um in the IR. Typically such a device puts out a continuous emission of from a few watts to several kilowatts. Determine the energy difference in eV between the two laser levels for this wavelength.

    2. A certain variation of He-Ne laser operates btwn two levels that are 3.655 x10^-19J apart. What color is the beam? comupte the wavelength.

    2. Relevant equations
    delta(E)=hc/^
    ^=wavelength

    3. The attempt at a solution
    1. answer is .117eV ..(6.63x10^-34)(3x10^8)/(10.6x10^-6)??but didn't get it
    2. answer is 543.5 nm( green)...3.655 x10^-19J =hc/^


    Please HELP! THanks!
     
  2. jcsd
  3. May 19, 2010 #2

    mgb_phys

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    Re: LASER Problems!! HELP NEEDED!

    Correct - the energy of a photon is E = h * frequency = h c / wavelenght

    As long as you get the numbers correct in your calculator thats all there is to it - be careful that if 'c' is in metres your wavelength will also be in metres
     
  4. May 19, 2010 #3
    Re: LASER Problems!! HELP NEEDED!

    c=3x10^8 right?
    can you explain more...??tHanks
     
  5. May 19, 2010 #4

    mgb_phys

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    Re: LASER Problems!! HELP NEEDED!

    Explain why E = h * frequency ?
    It's rather complex ( see http://en.wikipedia.org/wiki/Planck_constant)

    c = 3x10^8 m/s (remember units matter!)
    h = 6.6x10^-34 Js

    So energy (J) = h (Js) * frequency (1/s), check that the units cancel

    And since speed, c = frequency * wavelength you can rearrange this to give you
    Energy (J) = h (Js) c (m/s) / wavelength (m), again the units cancel out to give you J
     
  6. May 19, 2010 #5
    Re: LASER Problems!! HELP NEEDED!

    I already knew the equation...but I was not sure if I used the right numbers,,,??
    h=6.63x10^-34Js c= 3x10^8m/s

    whatelse??

    thanks
     
  7. May 19, 2010 #6

    mgb_phys

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    Re: LASER Problems!! HELP NEEDED!

    For the first part of the problem it asks for the energy in eV
    h = 4.14 x 10^-15 eV s
     
  8. May 19, 2010 #7
    Re: LASER Problems!! HELP NEEDED!

    ahhh got it! THank you! :)

    Can you please answer my other questions??(uncertainty problems?)
     
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