Question

An experimental set up similar to young's double slit experiment to observe the interference of light.

Here SS2 - SS1 = lambda/4

write down the conditions for

(1)constructive interfernece

(2) destructive interference in terms of path difference S2p - S1P = delta

Does the central fringe observed in the above set up lie above or below O . Give reason

Answer 1

I think constructive interference

Answer 2

I got this question in my physics board exam the previous day. And to the best I could figure how to go about this question is by making note of the fact that in normal YDS expt we get a path difference of 0 at the centre (bright spot) while in this scenario of λ/4 we get a path difference of λ/4 at the centre and we consequently deduct or add λ/4 to the normal constructive interference eqn interference.

I.e I =cos^2 { φ/2 + λ/4 } where φ can take the value of nλ for constructive interference.

I'm not sure though