
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!

Homework Help: Question About Diffraction Orders

  1. Jan 8, 2017 #1
    Light is normally incident on a double slit system. I'm asked to calculate the number of "orders(maxima)" visible on a screen placed in front of the slits. The light wavelength and slit separation are given. I understand that I can calculate the "order" from m=d/λ but does this number tell me the total maxima? Or am I to understand that there is a central maximum at m= 0 and then maxima at every ±m? For instance I got m=8.4; Does that mean I have 17 visible maxima or 8?


    2. Relevant equations

    3. The attempt at a solution
    I have calculated m but I don't quite understand it's meaning.
  2. jcsd
  3. Jan 8, 2017 #2

    Dr Transport

    User Avatar
    Science Advisor
    Gold Member

    There are two things that need to be considered here, the grating equation which you quote gives the angular distribution of the maxima from a single slit. Since you have a pair of slits, there is more going on here. The diffraction from a single slit gives an intensity [itex] \approx sinc^2()[/itex] envelop, the addition of the second slit modulated the intensity within this envelop.

  4. Jan 8, 2017 #3
    Okay, thanks for the input, I'm going off of Halliday and Resnick Ch 36.7. He says that the d is the spacing between the slits and I assume that if it's far enough away, dsinϑ=mλ will be sufficient to determine maxima for a double slit setup - I believe that the single slit analogue to this equation, asinϑ=mλ, where a is the slit width, gives orders m which are minima.

Have something to add?
Draft saved Draft deleted