Radar with a wavelength of 1.35 cm is incident on a thin protective coating cove

Question

Radar with a wavelength of 1.35 cm is incident on a thin protective coating covering a stealth fighter. The index of refraction of the thin coating is 1.84.

What is the wavelength of the radar waves in the thin coating?

            a) 0.73 cm

            b) 1.12 cm

            c) 1.35 cm

            d) 1.86 cm

            e) 2.48 cm

At what minimum thickness is the reflected radar a minimum (destructive interference)?

            a) 0.07 cm

            b) 0.15 cm

            c) 0.18 cm

            d) 0.29 cm

            e) 0.41 cm

How does the minimum thickness for constructive interference compare to the above answer?

            a) it is greater

            b) it is less

            c) it is the same

Explanation / Answer

here,

the wavelength of incident radar , lamda1 = 1.35 cm

The index of refraction of the thin coating , n2 = 1.84

using snell's law

the wavelength of the radar waves in the thin coating ,lamda2 = lamda1/n2

lamda2 = 1.35 / 1.84

lamda2 = 0.73 cm

the wavelength of the radar waves in the thin coating is a) 0.73 cm

let the minimum thickness for reflected radar having minimum distructive interference be t

for distructive interference,

2 * n2 * t = (m + 1/2 ) * lamda1

for minimum distructive interference , m = 0

2 * 1.84 * t = (1/2) *1.35

t = 0.18 cm

the minimum thickness for reflected radar having minimum distructive interference is c) 0.18 cm

as for constructive interference,

2 * n2 * t = (m ) * lamda1

the minimum thickness for constructive interference a) is greater than the above answer

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