A
thin film of acetone
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Solution: Click For PDF Version There is an additional phase change of
in each of the two rays which interfere after reflection from the
acetone film, as both reflections are from interfaces of greater
index of refraction of the transmitted side than that of the
incident side. Let the thickness of the acetone film be d
nm. The condition of destructive interference of nearly normal
incident waves of wavelength 600 nm on reflection
from the acetone film on a glass plate will therefore be
Therefore, the set of values of d when wave of wavelength 600 nm is used and destructive interference is observed will be
It is also given that when light waves of wavelength 700 nm are reflected from the film there is constructive interference. The condition for constructive interference is
Therefore, the set of values of d when wave of wavelength 700 nm is used and constructive interference is observed will be
The two conditions will be satisfied for
The thickness of the acetone film is 840 nm.
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is coating a thick glass plate
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Plane light waves of variable wavelengths are
incident normal to the film. When
one views the reflected wave, it is noted that complete destructive
interference occurs at 600 nm and
constructive interference at 700 nm. We
have to calculate the thickness of the acetone film.
