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Q. Blue light of wavelength $480$ nm is most strongly reflected off a thin film of oil on a glass slab when viewed near normal incidence. Assuming that the index of refraction of the oil is $1.2$ and that of the glass is $1.6$, what is the minimum thickness of the oil film (other than zero)?

Wave Optics

Solution:

$2 \mu t = n\lambda$
$\Rightarrow t =\frac{n\lambda}{2\mu}$
$\Rightarrow t =\frac{\lambda}{2\mu} = 200$ nm
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