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By an anodizing process, a transparent film of aluminium oxide of thickness `t = 250` nm and index of refraction `n_(2) = 1.80 ` is deposited on a sheet of polished aluminium What is the color of utenslis made from this sheet with observer in white light? Assume normal incidence of the light. |
Answer» We must find which colours in the visible region, having vacuum wavelengths from 400 nm (violet) to 700 nm (red), will interfere constructively and which destructively. From the problem, with `n_(1) = 1` (air) maximum constructive interference occurs for `lambda = (2(n_(2)//n_(1))t)/(m + (1)/(2)) = ((900 nm))/(m + (1)/(2)` `(m = 0, 2,...` Only the value corresponding to `m = 1`, that is, `lambda_(1) = 450 nm` (violet) is the visible range. we infer that the red-orange-yellow end of the spectrum will be strongly reflected, while the violet-blue end will be greatly diminished in intensity as compared with the illumination white light. |
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