Question

One face of a glass (μ = 1.50) lens is coated with a thin film of magnesium fluoride MgF2 (μ = 1.38) to reduce reflection from the lens surface. Assuming the incident light to be perpendicular to the lens surface, the least coating thickness that eliminates the reflection at the centre of the visible spectrum (λ = 550 nm) is about

(a) 0.05 μm

(b) 0.10 μm

(c) 1.38 μm

(d) 2.80 μm

Answer 1

Correct option (b) 0.10 μm

Explanation:

Reflection will be eliminated when light rays reflected from (air, film) interface and (film, glass) interface, interfere with each other destructively. Let the thickness of the film : x