Part A. In a Young's double-slit experiment the slit separation is mm, the screen is…
PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Interference and diffraction · Interference and diffraction
Optics and Photonics, Ch Two-beam interference and interferometry
Problem
Part A. In a Young's double-slit experiment the slit separation is d=0.40 mm, the screen is L=1.5 m away, and the sodium light used has λ=589 nm. A thin crown-glass plate of refractive index ng=1.50 and thickness t=10.0μm is placed over one slit only, adding an extra optical path (ng−1)t to that beam. No other change is made. (a) By how many fringe widths does the central fringe pattern shift? (b) What is this shift in millimetres on the screen? Part B. A Michelson interferometer has an evacuable gas cell of length ℓ=5.00 cm in one arm. As it is filled with carbon dioxide at λ1=633 nm, N1=142 fringes are counted passing the centre of the field. (a) Find the refractive index excess n−1 of the carbon dioxide at 633 nm. (b) Assuming n−1 is (to the precision needed here) the same at λ2=532 nm, predict the number of fringes N2 that would be counted filling the same cell at that wavelength.