Why exactly for this minima condition is: path difference = $(2n-1)\lambda/2,$ instead of $(2n+1)\lambda/2$?

And what is the starting order of minimal here?
Also, what does a negative path difference mean?


1 Answer 1


Let $m=n-1$. Then $(2n-1) = (2m+1)$. Therefore your two expressions are exactly the same if all integer values of $n$ are allowed; it is just a question of where you start the count.

If the path difference is $x_2 - x_1$ for two paths of lengths $x_1,\;x_2$ then a negative path difference means simply that $x_1 > x_2$. It means the first route was longer than the second, rather than shorter than the second.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

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