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

Question

Two towers on the top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. The longest wavelength of radio waves which can be sent between the two towers without appreciable diffraction effects is (A) 1.25 m (B) 12.5 m (C) 2.50 m (D) 0.250 m

Tardigrade Admin · Accepted Answer

Distance between the towers is 40 km. Height of the line joining the hills is d =50 m. Thus, the radial spread of the radio waves should not exceed 50 m. Since the hill is located halfway between the towers, Fresnel's distance can be obtained. Z P =20 km Aperture is a = d =50 m Fresnel's distance is given by the relation, beginarrayl Z P = a 2 / λ=2 × 104 λ= a 2 / Z P =12.5 cm endarray

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

$1.25 m$

$12.5 m$

$2.50 m$

$0.250 m$

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

1.25m

12.5m

2.50m

0.250m

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

$1.25 m$

$12.5 m$

$2.50 m$

$0.250 m$