a) Calculate the minimum thickness d of the film such that the resultant intensi

Question

a) Calculate the minimum thickness d of the film such that the resultant intensity of the light reflected back into the air is a maximum.

b) Calculate the minimum thickness d of the film such that the resultant intensity of the light reflected back into the air is a minimum.

c) In the problem above, the light reflected from each of the surfaces has its phase inverted at?

d) How would your answer change in the previous question if n film=1.7?

Please explain.

The surface of a glass plate is coated with a transparent thin film. A beam of monochromatic light (465 nm) is incident normally on surface S shown below. The beam is partially transmitted and partially reflected on both surfaces Si and S2 LI Air nr 1.00 Thin Film n 1.25 Glass ng 1.50

Explanation / Answer

wavelength of linght in the thin film

2=1/n2 = (465*10-9)/1.25 = 3.72*10-7 m

a)

2d1 = 2

d1 = 2 /2 = (3.72*10-7)/2 = 1.86*10-7 m

b)

2d1 = 2 /2

d1= 2/4 = (3.72*10-7)/4 = 9.3*10-8 m

c) n1<n2 ray from S1 experiences phase shift and n2 < n3 ray from S2 experiences phase shift

d) here n2>n3 so ray from S2 does not experience a phase shift

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