A film of water n2 = 1.33 below a thick glass plate n1= 1.65 are illuminated fro

Question

A film of water n2 = 1.33 below a thick glass plate n1= 1.65 are illuminated from above by light wavelength 470 nm at normal incidence. Below water is oil n3 = 1.20
Find minimum thickness of water if 100% is transmitted If instead water was 510nm, find wavelength A film of water n2 = 1.33 below a thick glass plate n1= 1.65 are illuminated from above by light wavelength 470 nm at normal incidence. Below water is oil n3 = 1.20
Find minimum thickness of water if 100% is transmitted If instead water was 510nm, find wavelength
Find minimum thickness of water if 100% is transmitted If instead water was 510nm, find wavelength

Explanation / Answer

for complete destructive interference of the relfected wave, necessary condition is

n*d=0.25*wavelength

where n=index of refraction of water

d=thickness of water

wavelength=470 nm

then using the given values,

thickness of water=0.25*wavelength/refractive index of water

=0.25*470*10^(-9)/1.33=88.345 nm

part b:

if thickness is 510 nm,

then 510*10^(-9)*1.33=0.25*wavelength

==>wavelength=510*10^(-9)*1.33/0.25=2713.2 nm

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