a) How far is the second dark fringe to the right of the central bright fringe in the double-slit interference pattern seen on a screen 4 m from the slits? The slits are separated by 0.4 mm and are illuminated with monochromatic light of wavelength 619 nm.
b) A layer of oil, with a refractive index of1.40798, 0.98315 mm thick, floats on water.
1. Light of vacuum wavelength 632.800 nm, emitted by a stabilized He-Ne laser, is reflected at normal incidence by the oil. How many wavelengths are contained in the light wave passing back and forth during the oil?