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To save money on making military aircraft invisible to radar, an inventor decides to coat them with a non-reflective material having an index of refraction of 1.20, which is between that of air and the surface of the plane. This, he reasons, should be much cheaper than designing Stealth bombers. (a) What thickness should the coating be to inhibit the reflection of 4.00-cm wavelength radar? (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?
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Final Answer
  1. $0.833 \textrm{ cm}$
  2. This is quite a thick layer and would be expensive to make consistently thick everywhere. It would also add significant weight.
  3. This idea is unrealistic, and even in the best case scenario where it isn't too expensive or heavy it would defend against only one frequency of radar. An easy countermeasure would be to use a different radar frequency.
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OpenStax College Physics Solution, Chapter 27, Problem 83 (Problems & Exercises) (5:59)

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