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`. Then the average distance of nth Fresnel zone will be at a distance …from the point of observation.

Options

A. `(bn lambda)/(2)`
B. `b-(n lambda)/(2)`
C. `b+(n lambda)/(2)`
D. `b-n lambda`

Answer

C

Explanation

The average distance of nth Fresnel zone from observation point will be at a distance `b+(n lambda)/(2)`.