Question

When does the double-slit interference have its first dark spot on either side of the central peak intensity?

when the paths d1 and d2 have the same length

when the paths d1 and d2 differ by half a wavelength

when the paths d1 and d2 differ by one wavelength

when the waves arrive in step, or “in phase,” with each other

Answer 1

I think it’s ‘ when the paths d1 and d2 differ by half a wavelength ‘ , am I correct?

Answer 2

Am I correct?

Answer 3

I think it's referring to the conclusions from Young's Interference experiment. By that analysis, you option B, the one you chose, should be correct.