Two parallel slits are illuminated with monochromatic light of wavelength 500 nm. An interference pattern is formed on a screen some distance from the slits, and the fourth dark band is located 1.68 cm from the central bright band on the screen.
(a) What is the path length difference corresponding to the fourth dark band?
(b) What is the distance on the screen between the central bright band and the first bright band on either side of the central band?