Question

Estimate how large can be the aperture opening to work with laws of ray optics using a monochromatic light of wavelength $450nm$ to a distance of around $20m$.

Answer 1

The distance at which this width equals the size of the aperture is called the Fresnel distance (in Fresnel diffraction method) which is given by

$z_F=\frac{a^2}{\lambda }$ where a is the aperture z_F is the distance acquired.

$\lambda =450\times {10}^{-9}m$

$z_F=20m$

$a^2=z_F\times \lambda$

$=20\times 450\times {10}^{-9}$

$=\sqrt{9\times {10}^{-6}}m$

$=3\times {10}^{-3}m$

$=0.003m$