A possible means for making an airplane invisible to radar is tocoat the plane w

Question

A possible means for making an airplane invisible to radar is tocoat the plane with an antireflective polymer. If radar waves havea wavelength of 2.50 cm and the index of refraction of the polymeris n = 1.40, how thick would you make the coating? (Assume that theindex of refraction of the plane is higher than that of thecoating.)
cm

Explanation / Answer

the reflection ware need to be destructive =>  minimum interfference the path difference : = 2ne    (e is thethick of coating) =>   = 2ne = ( k+1/2)   k = 0,1,2,... =>   e = (k+1/2)/2n = (k+1/2)*8.93x10^-3m      = (k+ 1/2)*0.893 cm .k =0 => e = 0.0465 cm .k=1 => e = 1.3395 cm ... we can choose k as large as possible,but the surface of theairplane is not the perfect plane=> should use thin coat it mean k is small (k=0,1 for example)

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