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!

Path diffrence to produce destructive intefrence

  1. Sep 7, 2014 #1
    1. The problem statement, all variables and given/known data

    A transparent flim of thickness t and reflective index n is placed in front of Y . Which one shows the new condition for destructive intefrence to occur ? the ans is (n-1) t = m λ
    . In my opinion , it should be (n-1) t = (m-0.5) λ ,
    because for destructive interference to occur , the path difference should be 0.5λ
    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Sep 7, 2014 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You seem to be pretty lazy (which may be a good quality) not filling in 2 and 3. Never mind. Could you be so good as to post the problem statement in facsimile too ? Is it a multiple choice thing (since it asks "Which one shows.."). And how do you know the ans ?
     
  4. Sep 8, 2014 #3

    NascentOxygen

    User Avatar

    Staff: Mentor

    Code (Text):
     
    From what you've written, I surmise that the question may actually be along these lines.....

    There is a point (which I'll denote as D) where there is a dark band. The piece of film is placed in front of Y. What is the condition for destructive interference to again occur at that point D?
     
  5. Sep 8, 2014 #4
    yes , this is roughly what the question means .
     
  6. Sep 8, 2014 #5
    In my opinion , it should be (n-1) t = (m-0.5) λ
    Am i correct?
    for destructive interfrence to occur , the phase difference must be (m-0.5)λ.
    i.e. destructive interfrence occur at 0.5λ (180 °) , 1.5λ (540°) ......
     
  7. Sep 8, 2014 #6

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Could you be so good as to post the problem statement in facsimile too ? Is it a multiple choice thing (since it asks "Which one shows.."). And how do you know the ans ?

    I think we can agree on that :smile:
     
  8. Sep 8, 2014 #7

    NascentOxygen

    User Avatar

    Staff: Mentor

    No.
    The total phase difference must be (m-0.5)λ, yes.
     
  9. Sep 8, 2014 #8
    since you said my (m-0.5)λ, is correct.... then why my (n-1) t = (m-0.5) λ is wrong?
     
  10. Sep 10, 2014 #9
    the other options are nt= mλ, (n-1) t = m λ , (n+1) t = m λ , and (n+1)t = 0.5mλ...
    my choice is (n+1)t = 0.5mλ .... Am i wrong ?
     
  11. Sep 10, 2014 #10
    the other options are nt= mλ, (n-1) t = m λ , (n+1) t = m λ , and (n+1)t = 0.5mλ...
    my choice is (n+1)t = 0.5mλ .... Am i wrong ?
     
  12. Sep 10, 2014 #11

    NascentOxygen

    User Avatar

    Staff: Mentor

    There is not much point just guessing. It's time to draw some diagrams and think about this really closely.

    Attach your diagrams so we can see how you go about it.
     
  13. Sep 10, 2014 #12

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    well celxis, O2 has me puzzled too. I don't think there's a phase jump involved, and I also think the path difference is (n-1)t (didn't mean to create the impression that it isn't, in post #6), so his (her?) no in post #7 must have some other reason. something about m that we all take for granted ?

    By the way, does the film have a reflective index n or an index of refraction n ?

    And I do hope your + in the last line of post 10 was a typo. Stick to the minus sign...
     
  14. Sep 10, 2014 #13
    SORRY , all。 please ignore my few post before it. my ans is still (n-1) t = (m-0.5) λ , but the ans is (n-1) t = m λ..
    there 're few choices :
    nt= mλ, (n-1) t = m λ , (n+1) t = m λ , and (n+1)t = 0.5mλ..

    reason for my choice :
    because for destructive interference to occur , the path difference should be 0.5λ
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Path diffrence to produce destructive intefrence
  1. Destructive inteference (Replies: 16)

Loading...