A source `S` and a detector `D` high frequency waves are a distance `d` apart on the ground. The direct wave from `S` is found to be in phase at `D` with the wave from `S` that is reflected from horizontal layer at an altitude `H`. The incident and reflected rayes make the same angle with the reflecting layer. When the layer rises a distance `h`, no signal is detected at `D` . Negle ct absorption in the atmosphere and find the relation between d,h, `H` and the wavelength `lambda` of the waves.

Answer

A, B, D

Explanation

`2 sqrt(H^(2) + d^(2)//4) - d = n lambda` ..(i)
Now, `2 sqrt((H + h)^(2) + d^(2)//4) - d = n lambda + (lambda)/(2)` ..(ii)
Solving these two equations, we get
`lambda = 2 sqrt(4(H + h)^(2) + d^(2)) - 2sqrt(4 H^(2) + d^(2))`