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Radio waves coming at anglealpha to veti...

Radio waves coming at `angle_alpha` to vetical are received by a radar after reflection from a nearby water surface and directly .what should be height of antenna from water surface so that it records a maximum intensity.(Wavelength =`lambda`)

Text Solution

Verified by Experts

The correct Answer is:
`(lambda)/(4cos alpha)`
Path difference =`BN+BA+(lambda)/(2)`
(because reflection occurs from denser medium)

`DeltaACB`
`(h)/(AB)=cosalpha`
`AB=(h)/(cosalpha),…(1)`
from rightangle`DeltaANB`
`(BN)/(AB)=cos2alpha`
`BN=ABcos2 alpha...(2)`
path difference=`(AB+ABcos2alpha)+(lambda)/(2)`
`lambda=AB(1+cos2 alpha)+(lambda)/(2)`
`(lambda)/(2)=(h)/(cosalpha)xx2cos^(2)alpha`
`(lambda)/(2)=2hcosalpha`
`h=(lambda)/(4cosalpha)`
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