When blue light of wavelength 460nm is incident upon a double-slit apparatus, it produces a second-order bright fringe (i.e, m=2) at a certain spot P on the screen.
(a) If point P is located at theta = 32degrees from the central maximum, what is the spacing between the two slits
(b) If you want there to be a dark fringe at point P using the same slits and screen, what wavelength of visible light (400 - 700nm) should you use instead of blue light?