1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Energy of a light quantum

  1. Jun 2, 2005 #1
    I'm looking for an expression for the "energy of a light-quantum in eV when the wavelength is in nanometers"

    and I'm kind of stumped :confused:

    anyone know this formula?


    thanks
     
  2. jcsd
  3. Jun 2, 2005 #2
    You can use [itex]E = \frac{hc}{\lambda}[/itex], where h is Planck's constant, c is the speed of light and [itex]\lambda[/itex] is the wavelength (in metres). This will give you an answer in Joules, all you need to do then is convert to eV (1 eV = 1.6 x 10^-19 J).
     
  4. Jun 2, 2005 #3
    ok so I can use [itex]E = \frac{hc}{\lambda}[/itex] X 1eV/1.6 x 10^-19 J

    What about the "in nanometers" part?

    The formula will work with a wavelength in nanometers, it will also work with any other size wavelengths..

    not sure what they are asking here.


    thanks
     
  5. Jun 2, 2005 #4

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    The formula applies regardless of the units. You just have to use consistent units. If you use MKS, the energy is measured in Joules (m^2kg/sec^2), c is in m/sec, distance in m and h in Jsec. A nanometer is [itex]10^{-9} metres[/itex].

    AM
     
  6. Jun 5, 2005 #5
    Is MKS just the same as SI units?
     
  7. Jun 5, 2005 #6
    I think MKS is meter-kelvin-seconds which is basically SI units.
     
  8. Jun 5, 2005 #7

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    MKS is metre-kilogram-seconds or SI units (Système International d'Unités) as opposed to CGS (=centimetre-gram-seconds) or FPS (=foot pound seconds).

    AM
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Energy of a light quantum
  1. Quantum Well energy (Replies: 1)

  2. Energy states quantum (Replies: 1)

  3. Quantum energy doubt (Replies: 12)

Loading...