4. In an interference experiment, reddish light of wavelength 6.0 x 102 nm passes through a double slit. The distance between the first and eleventh dark bands, on a screen 1.5 m away, is 13.2 cm. (a) Calculate the separation of the slits. (b) Calculate the spacing between adjacent nodal lines using blue light of wave- length 4.5 X 102 nm. 5. A parallel beam of light from a laser, with a wavelength 656 nm, falls on two very narrow slits, 0.050 mm apart. How far apart are the fringes in the centre of the pattern thrown upon a screen 2.6 m away? 6. Light of wavelength 6.8 X 102 nm falls on two slits, producing an interference pattern where the fourth-order dark fringe is 48 mm from the centre of the inter- ference pattern on a screen 1.5 m away. Calculate the separation of the two slits