Question

What is the thinnest film of MgF₂ (n = 1.38) on glass that produces a strong reflection for orange light with a wavelength of 600 nm?

Answer 1

Answer:

Thickness is 217 nm

Explanation:

For a thin film, constructive and destructive interference each has its own effects. Here constructive interference causes the light to be strongly reflected.  The thickness can be determined from

$2\times t\times n \times sin\theta=m\lambda$

here n is refractive index 1.38, m=1 , $\theta$=0, $\lambda$=600 nm

$t=\frac{600 \times 10^{-9}}{2\times 1.38} \\t=217 nm$