Question

For what distance is ray optics a good approximation when aperture is 3mm wide and wavelength is 500nm?

• A. 1500 m
• B. 500 m
• C. 118 m
• D. 18 m

Answer 1

The Correct Option is D

Ray optics is a good approximation when:
\[ z = \frac{a^2}{\lambda} \]
where $a = 3 \text{ mm} = 3 \times 10^{-3} \text{ m}$ and $\lambda = 500 \text{ nm} = 500 \times 10^{-9} \text{ m}$:
\[ z = \frac{(3 \times 10^{-3})^2}{500 \times 10^{-9}} \approx 18 \text{ m} \]