Question

The average path difference between two waves coming from third and fifth Fresnel zones of a wave front at the centre of the screen is :

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

Answer 1

Answer: (C)

$\lambda$

The third and fifth fresnel zone differ in phase by $2\pi$. Thus as $2\pi$ corresponds to path difference of $\lambda$.