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Homework Help: Rate of Photon Strike

  1. Apr 11, 2005 #1
    Monochramatic light of wavelength 300 nm is incident normally on a surface of area 4 cm squared. If the intensity of the light is 15x10^-2 W/m^2, determine the rate at which photons strike the surface.

    Honestly when reading this I thought I missed something in the chapter. A wave of 300nm strikes a metal surface that is 4 centimeters squared. The light intensity strikes with 15x10^-2. Im just lost on how to start it because I havent seen anything like it in this chapter.
  2. jcsd
  3. Apr 11, 2005 #2
    I = power/ area
    power = energy / time
    energy of each photon is given by hc/lambda
    so the enrgy of a certain number,n of photons is nhc/lambda
    im not quite sure how to eliminate the time in the equation you will get... perhaps someone else will helpm since i too am curious on how to solve something like this
  4. Apr 11, 2005 #3


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    The rate of photons means #of photons each second.The # of photons can be computed by dividing the transfered energy to the surface by the energy of one photon...That "/s" is gotten by diving the power (energy in unit time) and not the energy.

    [tex] \mbox{No.photons \ per \ s}=\frac{15\cdot 10^{-2} \ \frac{W}{m^{2}}\cdot 4\cdot 10^{-4}m^{2}}{\frac{hc}{\lambda}} [/tex]

    Last edited: Apr 11, 2005
  5. Apr 11, 2005 #4
    ok sorry i dont mean to hijack your thread but dexter can u take a look at my thread on index of refraction i nteh college level forum?
  6. Apr 11, 2005 #5
    Thanks, that helps a lot..made it a lot clearer
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