# Coating in Lenses!

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 $$MgF_2 (n = 1.38)$$. What should the thickness of the film ($$d$$ in Angstrom) be so that at the center of the visible spectrum $$(5500 Angstrom)$$, there is maximum transmission?

Note : Round off the value of $$d$$ to the nearest 1000. (ex. if the value comes out to be 5997, then the answer should be 6000)

Source - NCERT Exemplar Problems

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