Question

The source is at some distance from an obstacle. Distance between obstacle and the point of observation is $b$ and wavelength of light is $\lambda$. The distance of $n^{th}$ Fresnel Zone from the point of observation is :

• A. $\frac{bn\lambda }{2}$
• B. $b-\frac{n\lambda }{2}$
• C. $b+\frac{n\lambda }{2}$
• D. $b-n\lambda$

Answer 1

Answer: (C)

$b+\frac{n\lambda }{2}$

If the distance between the obstacle and the point of observation is 'b' then the distance of the nth Fresnel Zone = $b+\frac{n\lambda }{2}$ from the point of observation.