Question

What happen when we cover one slit in ydse?

Answer 1

The two-slit interference pattern will be replaced by a single-slit diffraction pattern. This pattern was already superimposed on the dark and bright bands of the interference pattern - so the bands disappear, leaving behind much wider bands. Averaging over the whole screen, it will only be half as bright, but it will seem less so, because there are fewer areas of complete darkness than before, so the bright areas are a bit more spread out, and so, diluted.