My professor derived the conditions for maxima and minima on the screen by dividing the slits into equal parts.I ll try to summarize it:
- The optical path distance between secondary waves emanating from the top and bottom of the slits is asinθ.
2.If asinθ=2 λ then the aperture AB can be imagined to be divided into 4 equal parts and the waves from the corresponding points separated by a distance a/4 in the two halves of each of the slit will differ in path by λ/2 and this gives position of minimum intensity.
My question is why can't we divide the slit into two equal parts such that the optical path difference between waves emanating from corresponding points in each half differ by λ and hence interfere constructively leading to maximum intensity?