1. Light from a helium-neon laser (l=650 nm) is used to illuminate two narrow slits. The interference pattern is observed on a screen 2.12 m behind the slits. Twelve bright fringes are seen, spanning a distance of 49 mm. What is the spacing (in mm) between the slits? lamda=650x10^-9 m L=2.12 m Ym=49x10^-3 m= 12 d=solving for d=mL(lamda)/Ym= .03375 mm why doesnt that work? 2. A 0.24-mm-diameter hole is illuminated by light of wavelength 476 nm. What is the width (in mm) of the central maximum on a screen 1.5 m behind the slit How do I do this since it has a diameter, I can't find it in the book anywhere 3. A 578 line/mm diffraction grating is illuminated by light of wavelength 599 nm. How many bright fringes are seen on a 2.73-m-wide screen located 3 m behind the grating d=1/(578x 10^-3) lamda=599x10^-9 Ym=2.73 m L=3 m m=Ym*d/(lamda*L) All these ways of solving them doesn't work why is that?