To ensure almost 100% transmittivity, photographic lenses are often coated with a thin layer of dielectric material. The refractive index of this material is intermediated between that of air and glass (which makes the optical element of the lens). A typically used dielectric film is MgF2 (n=138). What should the thickness of the film be so that at the centre of the visible spectrum (5500 Å) there is maximum transmission.

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Vishal Baghel | Contributor-Level 10

7 months ago

This is a Long Answer Type Questions as classified in NCERT Exemplar

Explanation- refractive index = 1.38 refractive index = 1.5

^{$λ = 5500 A$ 0}

Consider a ray incident at an angle i. A part of this ray is reflected from the air-film interface And apart refracted inside.

This is partly reflected at the film-glass i

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