Question

The phase difference between two waves from successive half period zones or strips is :

• A. $\frac{\pi }{4}$
• B. $\frac{\pi }{2}$
• C. $\pi$
• D. zero

Answer 1

The correct option is C $\pi$

The half period zone is provided by an optical device known as zone plate. It is simply a plane parallel gloss plate having concentric circles of radii accurately proportional to the square roots of the consecutive natural numbers 1,2,3 ... etc. The area is given by $\pi {\gamma }^2$. Hence the
areas are $\pi ,2\pi ,3\pi ,4\pi$,---
The phase difference is thus $\pi$ between each successive half period zones of strips.