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?