# Thin Film Interference

## Homework Statement

A researcher measures the thickness of a layer of benzene (n = 1.50) floating on water by shining monochromatic light onto the film and varying the wavelength of the light. She finds that light of wavelength 565nm is reflected most strongly from the film. What does she calculate for the minimum thickness of the film?

Values:
λ = 565*10^-9m
n(benzene) = 1.50
n(water) = 1.33

## Homework Equations

I have tried both of these equations:
2t = mλ
2t = ½mλ

## The Attempt at a Solution

Subbing in the values needed, I get
t = (1 * 565*10^-9) / 2
= 2.825*10^-7m
or
t = (½ * 1 * 565*10^-9) / 2
= 1.4125*10^-7m

ehild
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## Homework Statement

A researcher measures the thickness of a layer of benzene (n = 1.50) floating on water by shining monochromatic light onto the film and varying the wavelength of the light. She finds that light of wavelength 565nm is reflected most strongly from the film. What does she calculate for the minimum thickness of the film?

Values:
λ = 565*10^-9m
n(benzene) = 1.50
n(water) = 1.33

## Homework Equations

I have tried both of these equations:
2t = mλ
2t = ½mλ
These are not the relevant equations. Do you think the refractive indices do not count?

I wasn't too sure.
Would that mean I would have to calculate the relevant wavelength through the film?
Would that mean:
λfilm = λ / n(benzene) (λ = 565 and n(benzene) = 1.5)
λfilm = 3.77*10^-7

*EDIT* I realise the mistake I made, and I did need to calculate λfilm.
The answer I got was 9.42*10^-8 and that was correct.

Last edited:
Michael Hussey
How did you get the correct answer? Please do show the working out. I am lost in this question. Thank you heaps

Michael Hussey
Nevermind, i have figured out the answer.

Michael Hussey
Can you please demonstrae your working for Q9,10,11 if you remember or its available thanx