Question

Fresnel’s zones are known as half period zones because the path difference between consecutive zones is

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

Answer 1

The correct option is A $\frac{\lambda }{2}$


$\varphi =\frac{2\pi }{T}t=\frac{2\pi }{T}\left(\frac{T}{2}\right)$
$\varphi =\pi ;\varphi =\frac{2\pi }{\lambda }x$
$\pi =\frac{2\pi }{\lambda }$
$x=\frac{\lambda }{2}$