Question

An aperture of size a is illuminated by a parallel beam of light of wavelength $\lambda$. The distance at which ray optics has a good approximation is

• A. $\frac{a^2}{\lambda }$
• B. $\frac{\lambda }{a^2}$
• C. $\frac{\lambda }{a}$
• D. $\frac{{\lambda }^2}{a}$
• E. $a^2\lambda$

Answer 1

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

An aperture of size a is illuminated by a parallel beam of light of wavelength $\lambda$. The distance at which ray optics has a good approximation is $\frac{a^2}{\lambda }$. This is the Fresnel distance.