A nonreflective coating (n = 1.41) covers the glass (n = 1.52) of a camera lens.

Question

A nonreflective coating (n = 1.41) covers the glass (n = 1.52) of a camera lens. Assuming that the coating prevents reflection of yellow-green light (wavelength in vacuum = 569 nm), determine the minimum nonzero thickness that the coating can have. nm A slit has a width of W_1 = 4.3 times 10^-6 m. When light with a wavelength of lambda_1 = 541 nm passes through this slit, the width of the central bright fringe on a flat observation screen has a certain value, with the screen kept in the same place, this slit is replaced with a second slit (width W_2), and a wavelength of lambda_2 = 409 nm is used. The width of the central bright fringe on the screen is observed to be unchanged. Find W_2. W_2 = For a wavelength of 420 nm, a diffraction grating produces a bright fringe at an angle of 26 degree. For an unknown wavelength, the same grating produces a bright fringe at an angle of 44 degree. In both cases the bright fringes are of the same order m. What is the unknown wavelength? nm

Explanation / Answer

22. wavelength = 569nm

index of refraction n = 1.41

formula wavelength/2 = 2 n t

thickness t = wavelength/4n = 569/ 4 x 1.41

=100.89 nm

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