Question 82 of 295
A transparent film of refractive index, 2.0 is coated on a glass slab of refractive index, 1.45. What is the minimum thickness of transparent film to be coated for the maximum transmission of Green light of wavelength 550 nm . [Assume that the light is incident nearly perpendicular to the glass surface.]
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Answer: (A) 137.5 nm
For transmitted green light to be maxima, reflected green should be minima.
$\begin{aligned}
& \Delta \mathrm{P}=2 \mu_0 \mathrm{t}=\mathrm{n} \lambda \\
& \Rightarrow \mathrm{t}=\frac{\mathrm{n} \lambda}{2 \mu_0} \therefore \mathrm{t}_{\min }=\frac{\lambda}{2 \mu_0}=\frac{550}{2 \times 2}=137.5
\end{aligned}$
