Question

Two towers on the top of two hills are 40km apart. The line joining them passes 50 m above a hill halfway between the towers. The longest wavelength of radio waves is :

• A. 1.25 m
• B. 0.125 m
• C. 2.50 m
• D. 0.250 m

Answer 1

Answer: (B)

0.125 m

Answer 2

Using, $z_{F} = \frac{a^{2}}{\lambda}$ or $\lambda = \frac{a^{2}}{z_{F}}$

$\therefore\lambda = \frac{(50)^{2}}{2 \times 10^{4}} = 1250 \times 10^{- 4} = 0.125m$