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  • Two towers on top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. What is the longest wavelength of radio waves, which can be sent between the towers without appreciable diffraction effects?

Q10.18 Two towers on top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. What is the longest wavelength of radio waves, which can be sent between the towers without appreciable diffraction effects?

Answers (1)

best_answer

Given,

Distance between two towers = 40km

size of aperture = a=50m

Now,

As we know

Fresnel's distance is equal to half of the distance between towers

Z_f=\frac{40}{2}=20km

 

Also from the formula:

Z_f=\frac{a^2}{\lambda}=20m

\lambda=\frac{a^2}{Z_f}=\frac{50^2}{20*10^3}=12.5cm

Hence this is the required longest wavelength of the radio wave, which can be sent in between the towers without considerable diffraction effect.

Posted by

Pankaj Sanodiya

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