Anti-reflective coatings on lenses use thin-film interference to eliminate the reflection of a particular color. Suppose a glass lens (ng = 1.55) is covered with a thin film (nf = 1.35) to prevent green light (λ = 521 nm) from being reflected.

a. Write an expression for the minimum thickness the film can have, t.
b. Calculate the minimum thickness, t, in nanometers?

Given:

According to the question,

The optical path difference will be:

→

The condition for destructive interference of reflected light will be:

→

For minimum thickness,

then,

→

hence,

The minimum thickness will be:

→

By putting the values, we get

Thus the responses above is right.

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Answer with Explanation:

We are given that

a.We have to find the expression for  the minimum thickness the film can have ,t.

Condition for destructive interference

For minimum thickness m=0

Then,

b.Substitute the values