A parallel beam of white light falls from air on a thin film in air whose refractive index is equal to 
.The angle of incidence i = 60°, what must be the minimum film thickness (in nanometer) if the reflected light is most intense for λ = 6000 Å ?
Text Solution
Verified by ExpertsThe correct answer is:
CHECK THE SOLUTION.
Sol. 1 sin 30° = 
sin r
⇒ r = 30°
Optical path diff. = 2 μ t sec r – 2t tan r sin i
= 
t sec 30° – 2t tan 30° sin 60°
= 4t – 2t 
. 
= 3t
Phase diff. = π due to reflection of ray 1
∴ for constructive interference, 3t = 
= 1000 Å = 100 nm
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