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  • To ensure almost 100 per cent transitivity, photographic lenses are often coated with a thin layer of dielectric material. The refractive index of this material is intermediated between that of (which makes the optical element of the lens).

To ensure almost 100 percent transitivity, photographic lenses are often coated with a thin layer of dielectric material. The refractive index of this material is intermediated between that of (which makes the optical element of the lens). A typically used dielectric film is MgF2 (n = 1.38). What should the thickness of the film be so that at the center of the visible spectrum (5500 Å) there is a maximum transmission

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Explanation:-

The phenomenon of maximum transmission due to the coating of dielectric material on lenses is due to constructive interference. This interference arises because the dielectric film causes a phase shift in the light waves as they pass through it.

IA is an incident ray at point A is such that the incident angle I is formed from air to the film surface.

AR1 and AD are the reflected and refracted rays, respectively. D is the point on which the partial reflection of the glass and film interface. CR2 and AR1 are parallel.

\\\mu (AD + CD) - AB\\ AD = AC = \frac{d}{\cos r}\\\\ d \tan r = \frac{AC}{2}\\\\ d = 1000 \AA

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Gurleen Kaur

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