An airplane is made invisible to radar by coating it with a layer of an antireflective polymer having an index of refraction of 1.50.What is the thickness of the polymer if the maximum wavelength of radar waves for which the plane is made invisible is 4.0 cm?

Question

Quizplus · Accepted Answer

For maximum destructive interference, the thickness of the polymer layer should be a quarter of the wavelength in the medium. The wavelength in the medium ($\lambda'$) is given by $\lambda' = \lambda / n$, where $\lambda$ is the wavelength in air (4.0 cm) and $n$ is the index of refraction (1.50). Thus, $\lambda' = 4.0 \, \text{cm} / 1.5 = 2.67 \, \text{cm}$. The thickness for maximum destructive interference is $\lambda' / 4 = 2.67 \, \text{cm} / 4 = 0.667 \, \text{cm} = 6.7 \, \text{mm}$.

An Airplane Is Made Invisible to Radar by Coating It