1.What is the wavelength of the light entering an interferometer if 648 bright fringes are counted when the movable mirror moves 0.205 mm?
2.What is Brewster's angle for an air-alcohol (n = 1.36) surface?
3.A total of 33 bright and 33 dark Newton's rings (not counting the dark spot at the center) are observed when 530 nm light falls normally on a planoconvex lens resting on a flat glass surface (Fig. 24-31). How much thicker is the center than the edges?
- 魏王將張遼Lv 71 decade agoFavorite Answer
(1) According to the given from the question, it is known that for a distance of 0.205 mm, the path difference has changed by 648λ, so:
648λ = 0.205 × 10-3
λ = 316.4 nm
(2) Using the formula n = tan θp, where θp is the Brewster's angle:
tan θp = 1.36
θp = 53.67°
(3) The equation for the radius of the mth Newton's bright ring goes as follows:
R is the radius of curvature of the lens the light is passing through,
m is 1,2,3... which is dependent upon the number of light spots,
λ is the wavelength of the light passing through the glass.
So, for the 33rd ring, x33 = √(33.5 λR)
Also, with the aid of following diagram:
and the formula x332 = 2Rt where t is the central thickness of the lens.
So, 33.5 λR = 2Rt
t = 16.75 λ
= 8.88 μm
So the center is 8.88 μm thicker than the edges.Source(s): My Physics knowledge