I'm studying wave interference and having trouble to understand some concepts. I would like to ask what would happen in the 2 situations below Image 1 [Broken] Image 2 [Broken] Both waves are identical, have the same frequency, amplitude and velocity. They are polarized on the direction shown (first one oscilates going out of the screen, second one on the plane of the screen). At the red circle they interfere construtively (that means A.Cos(...) are equal). The waves have perpendicular propagation directions. What will be the amplitude on the red points? I would say 2A for the first image and A √2 for the second. Is it right? I'm asking because on the slit experiment (OEM interference) my book (and everybody) seems to treat constructive interference as 2A, ignoring the angle between the waves. Why is that?