0
$\begingroup$

Two very narrow slits are spaced apart and are placed 35.0 cm from a screen. What is the distance between the first and second dark lines of the interference pattern when the slits are illuminated with coherent light with λ= 550nm

I'm not asking for an answer for this because I understand the method. I am confused by the theory behind it. When I consulted the solutions manual for this question, they say the first dark line occurs at m = 0 (where m is the order of the image), whereas I thought it occurred at m = 1. Why is this so?

|cite|improve this question
$\endgroup$
  • $\begingroup$ Can you define $m$ please? There is a point of constructive interference in line with the direction of the incident source, yes. $\endgroup$ – Floris Apr 24 '16 at 17:50
  • $\begingroup$ And of course one has to define "first" dark line - I presume it is counting up from the center out... $\endgroup$ – Floris Apr 24 '16 at 17:51
  • $\begingroup$ Different people can mean different things by $m$. Some people start counting at 0, others at 1 ... in any event, we need to know what it means to you. $\endgroup$ – garyp Apr 24 '16 at 19:56
  • $\begingroup$ Sorry about that. In this instance "m" is referring to the order of the image. I'll amend my question. $\endgroup$ – BigBoss Apr 25 '16 at 11:17
0
$\begingroup$

It's not m=0. The sin of d ( or the angle that you will find the dark spots) is equal to ( m+1/2) times the wavelength. m=0,1,2,3.........

|cite|improve this answer
$\endgroup$
  • $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review $\endgroup$ – Jon Custer Apr 24 '16 at 21:14
  • $\begingroup$ Sure it does. My answer gave the correct formula for the dark spots. The OP thought it occurred at in m=1. There is more to the formula than that. How else would you have answered it? $\endgroup$ – Bill Alsept Apr 24 '16 at 22:51
0
$\begingroup$

Apologies everyone, I misunderstood this question greatly. It's talking about the first dark fringe (or the zeroth order dark fringe) which occurs in between 0 and 1. I understand now.

|cite|improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.