You are considering different set ups of a thin film between two materials. Cons

Question

You are considering different set ups of a thin film between two materials. Consider what happens when light starts in the top material (e.g. air for part i), will light reflecting off of surface A undergo a phase shift, will light reflecting off of surface B undergo a phase shift? Then consider what happens when light starts in the bottom material (e.g. glass for part i).

Light Starts in the Top Material Light

Residue from fingers on smart phone’s screen:

Is there a phase shift at surface A? …

at surface B?

Light Starts in the Bottom Material

Is there a phase shift at surface B?

… at surface A?

Explanation / Answer

1.For Air i.e when the light starts at air

a.At surface A as for skin oil n= 1.43 > n 1 for air

So ,there will be a shift equal to lambda/2 here lambda is the wavenegth of light

b.At surface B again n for glass = 1.51> n for skin oil 1.43 and considering the width as 't' there will be a total shift of (2t + (lambda/2))

we can calculate the relative shift by substracting the individual shift.

2. considering the surface where the light starts at glass

a.As for glass n = 1.51 > skin oil n =1.43 then no shift i.e 0

b. again from skin oil n =1.43 > n for air as 1 so 0 shift

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