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Energy of the photon

  1. Sep 23, 2007 #1
    1. The problem statement, all variables and given/known data

    An excited atom emits a photon of red light with a wavelength of 701. nm, what is the energy of the photon?----> _________________J


    2. Relevant equations

    and for this, my application was

    firstly get landa from formula of c=landa * nu

    and then landa * h, which is planck's constant which is 6.626e-34.

    since my wavelength is 701 nm, it can be 701e-9 in order to change to meter format.

    so my final application would be {(2.998e8m/s)/(701e-9m)} * ( 6.626e-34J*s)= 2.83e-19 (after rounding up to get significant figures which is 3 digits from 701nm)



    3. The attempt at a solution

    2.83e-19
     
  2. jcsd
  3. Sep 23, 2007 #2
    1. Units! 2.83e-19 even if it's correct numerically is still wrong. You *need* to always have units.

    2. Stay in symbols! Write down [tex]E = \frac{hc}{\lambda}[/tex], then just substitute in the numbers, after conversion to correct units.

    (Btw, it's "lambda" not "landa")
     
  4. Sep 23, 2007 #3
    i did put J (unit) at the end as well and it kept telling me wrong. did i do any conversion wrong?
     
  5. Sep 23, 2007 #4
  6. Sep 23, 2007 #5
    oh, i got it.
    the answer needed to be negetive because the question says "emits". so answer had to be negative. i replaced the answer with -2.84e-19 and it was correct. thank you for the help. now i can go to bed.
     
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