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) $ \dfrac{\lambda }{2} $
(B) $ 2\lambda $
(C) $ \lambda $
(D) $ 4\lambda $

Hint: The Fresnel zone can be defined as the area around the visual line of the sight that radio waves which are spread out into the air after which they leave the antenna. Here, we will find the difference between the third and the fifth Fresnel zones.

Complete answer:
In simple words, the Fresnel zone can be defined as the three-dimensional elliptical region which is between the transmit antenna and the receive antenna is called the Fresnel Zone.
The third region surrounds the second region and similarly the fifth region surrounds the fourth region. The third and the fifth Fresnel zones have the difference in phase angle by this angle difference corresponds to the path and the difference of $ \lambda $
From the given multiple choices, the option C is the correct answer.

Note:
The Fresnel Zone is very important since when an installation of the wireless point to point bridge is designed and installed where in generally the line of sight is required and this clearance is known as the Fresnel zone.