In a Young's double-slit experiment, a parallel beam of wavelength 4000 Å is incident on the slits at 30° as shown. Slit separation is 10 mm and the screen is 1 m away.

Question

G1 Physics · Accepted Answer

For this obliquely illuminated YDSE, the ordinary fringe width is β=λD/d. The incoming beam also creates an initial path difference d sin30° between the slits, which shifts the entire fringe system. Each sub-question is obtained by combining this initial path difference with the usual observation-path difference dy/D.