Interference in a soap film (a) Calculate the minimum thickness of soap bubble f

Question

Interference in a soap film (a) Calculate the minimum thickness of soap bubble film n = 1.46, that will result in constructive interference in the reflected light if the fil is illuminated by 600 nm light (free space wave length) (b) What other film thicknesses will produce constructive interference? Nonreflecting coating on solar cells Solar cells are often coated with transparent thin film such as silicon mono oxide SiO n = 1.45. A silicon solar cell n =3.5 is coated with silicon monoxide. Determine the minimum thickness of the film that will produce least reflection at a wave length of 550 nm, center of the visible spectrum.

Explanation / Answer

given n = 1.46
a. for constructive interference
   2t = (m + 1/2)lambda/n
   where lambda is the wavelength of light
   n is refractive index
   m is a whole number
   t is the thickness
   for minimum thickness, m = 0
   lambda = 600 nm = 600*10^-9 m
   2t = 0.5*600*10^-9/1.46
   t = 102.739 nm
b. for m = 1
   t = 308.219 nm
   f= 2
   t = 513.698 nm
   for m = 3
   t = 719.78 nm etc

c. SiO n = 1.45
   silicon solar cell, n' = 3.5
   lambda = 550 nm
   for destructive interferecen the reflection is least
   so for destructive interference
   2t = m*lambda/n
   for minimum thickness
   t = 0.5*1*550/3.5 = 78.571 nm

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