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Homework Help: Laser Light

  1. May 27, 2004 #1
    I do not know how to do the second part of this question. I never learned this.

    A laser used to weld detached retinas puts out pulses of 640 nm light, 25 ms long, which average 0.50 W output during a pulse.
    i) how much energy can be deposited pre pulse?
    ii) If the energy of a light particle (photon) is about 3 * 10^-19 J, how many photons does each pulse contain?

    I do not know how to get this.
  2. jcsd
  3. May 27, 2004 #2
    If you have the energy from the first part (E=Pt), and you know how much energy is in each photon, you just have to figure out how many photons give you that energy.

    Etotal=N * Ephoton
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