# Homework Help: Thin film interference - Minimum thickness

1. May 11, 2013

### Saitama

1. The problem statement, all variables and given/known data
A lens ($\mu$=1.5) is coated with a thin film of refractive index 1.2 in order to reduce the reflection from the surface at $\lambda=480 nm$. Find the minimum thickness of the film which will minimize the intensity of reflected. [Assume near normal incidence]

2. Relevant equations

3. The attempt at a solution
I don't really know how to begin with this. It looks to me that this is related to thin film interference but I have never dealt with three different mediums while solving problems related to this.

2. May 11, 2013

### Staff: Mentor

It's just thin film interference. All you need to worry about are the reflections from the top and bottom surfaces of the film.

3. May 11, 2013

### Saitama

Is it simply a plug and chug question then? :tongue2:

I get the right answer using the formula $2\mu d=(n+1/2)\lambda$ and putting $n=0$. I get $d=10^{-7} m$. Thanks Doc Al!