Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Young's double slit and coherent light

  1. Mar 28, 2013 #1
    Hello all,
    I was looking through my textbook on the double slit and it talks about constructive interference occurring at path differences of m [itex]\lambda[/itex] and destructive interference occurring at path differences of (m + 1/2) [itex]\lambda[/itex] where m is an integer. This is obvious if the waves leave the 2 slits in phase, however the book states that it is not necessary for the waves to be in phase, just for them to be coherent (ie. constant phase difference). Now I understand how the fringe pattern would form here but I fail to understand how the above conditions can be true as for the two to be in phase, one would have to travel further to be in phase at the arbitrary point P. Is this a textbook oversight or am I missing something?
    Thanks,
    Dom
     
  2. jcsd
  3. Mar 28, 2013 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    If the incoming light has different phases at the slits, the points of constructive/destructive interference will be different as well, right.
     
  4. Mar 28, 2013 #3
    So the constructive interference only occurs at m [itex]\lambda[/itex] if in phase at the slits as I assumed?
     
  5. Mar 28, 2013 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Right.
     
  6. Mar 28, 2013 #5
    I see, thanks very much for clearing that up.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Young's double slit and coherent light
Loading...