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: Optics question involving light waves

  1. Oct 10, 2012 #1
    I tried to solve this question. NO idea if i'm even on the right track.

    1. The problem statement, all variables and given/known data

    Suppose irradiation of a 100W light bubble (very small - be assumed as point source)
    is homogeneous in all directions. Because of low efficiency, only 2% of the electrical
    energy will be converted to light energy in the visible range, among which only 10%
    passes through the filter. The filter is located at 1m away from the bubble and followed
    immediately by a large 1mm-squared photo detector.
    Assume that the electrical field of light traveling in the filter is given by:

    E(r) = Eo(r)[(∏*10^15) (t - r/(.65c))]

    1. Write the mathematical equation of E(r) (ignore the surface loss of the filter).
    2. Calculate the frequency of light?
    3. Calculate the wavelength of light?
    4. What kind of color filter is used?
    5. What is the index of refraction of the filter?
    6. What is the intensity of light detected (assume quantum efficiency is 0.65)?
    7. How many photons will be detected per second?
    8. Is the filter likely to have a normal or abnormal dispersion in the filtering wavelength range?

    2. Relevant equations

    [itex]\upsilon[/itex] = frequency
    [itex]\lambda[/itex] = wavelength
    c= speed of light
    [itex]\epsilon[/itex]o = vacuum permittivity

    3. The attempt at a solution

    1. E(r) = Eo(r)[ωt - r/c]
    2. E=hc/[itex]\lambda[/itex]
    3. [itex]\lambda[/itex][itex]\upsilon[/itex] = c use [itex]\lambda[/itex] from Q2. to solve for [itex]\upsilon[/itex]
    4. colour depends on the wavelength
    5. 0.65/c = n filter / n of medium
    make medium air . Therefore n of medium= 1 and nfilter = 0.65
    6. I = [(.65cn[itex]\epsilon[/itex]o)/2] * E^2
    plug in and solve for I
    7. NO idea
    8. NO idea.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 10, 2012 #2
    by any chance, is this for biosensors?

    I'm trying to figure out the problem myself. I got something similar for 1.
    I'm working on 2. Do you know if we're supposed to figure this out for filtered light or unfiltered?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook