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AS physics question Please Help its hard

  1. Mar 16, 2004 #1
    Here are two questions I am stuck on:
    1. How many visible photons are produced per second from a 2Watt lamp? It says the range of the wavelengths is near 5x10^-7m. I tried this and got 3.33x10^33Hz but apparently thats wrong so please help me.

    2. A photon of frequency 6x10^14Hz explores a path 6m long. Find the time of travel and the number of rotations of the phasor. This one I dont have a clu how to start but if I get the first answer I can easily work out the number of rotations of the phasor.

    Please help me as I am really stuck...physics is really hard on this AS course. Thanks for all your help

    meawinner
     
  2. jcsd
  3. Mar 16, 2004 #2
    Mea, do you know the energy of each photon is given by Planck's constant times the frequency?

    2 Watts is power = energy per second.
     
  4. Mar 16, 2004 #3
    Yup

    Yeah i tried this and thats where i got the 3.33blah blah blah.... answer. I used 2W = 2joules per second and therefore if its one second it 2 joules, i put this in E=hf and it came out wrong as thats not the answer in my text book. Dont say why cant i just copy it because the teacher will know if there is no working. But thanks anyway. Do you know any other way?
     
  5. Mar 16, 2004 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Re: Yup

    Try again. First find the energy of a single photon, using E =hf. (Hint: First change the given wavelength into frequency, using the wave equation: v = fλ.)
     
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