1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Intensity of a plane monochromatic light wave

  1. Apr 29, 2007 #1
    1. The problem statement, all variables and given/known data
    A plane monochromatic light wave passes from a source inside an aquarium tank through water of index of refraction 1.33, then, at normal incidence, through a flat pane of glass of index 1.5 into air. Calculate the ratio of the intensity of the emergent light wave to that of the wave in the water. Assume that the permeabilities are all mu_o

    2. Relevant equations

    so, I found two equations I thought would be useful for this calculation:
    I_I= .5*E_1*v_1*((E_0_I)^2)*cos(theta_I)
    I_T= .5*E_2*v_2*((E_0_T)^2)*cos(theta_T)

    I_I= the incident intensity
    I_T= the transmitted intensity
    E_1= the permittivity of medium one
    E_2= the permittivity of medium two
    v_1= the velocity of the light in medium one
    v_2= the velocity of the light in medium two
    E_o_I= the max electric field of the incident wave
    E_o_T= the max electric field of the transmitted wave
    (in other words, the _ denotes subscript- I can't find an equation writer- is there one on this site? where do I find it?)

    3. The attempt at a solution

    I think that if these equations will yeild the correct answer, that the calculation is strait forward; However, i'm not sure that they use all the information provided. I know that I will use the indeces of refraction to find the velocities v_1 and v_2, but what about the assumption that all mu=mu_o?
    Do these equations assume that to be the case? Also, using these equations, I would not need the index of refraction of the thin pane of glass, and the description of the problem gives that information.

    More concisely, are these the right equations? If not, then what equations would I need to figure this out?

    Thanks alot!
  2. jcsd
  3. Apr 29, 2007 #2


    User Avatar
    Homework Helper

    I think you're overcomplicating this. When a wave hits an interface between two materials of different indices of refraction, a portion of its intensity is transmitted, and a portion is reflected. Do you have these equations? They are derived from continuity of certain components of the electric and magnetic fields at the boundary.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook