# Phase differences of light and multiples of lambda

1. Nov 11, 2009

### h00di3

Hello All,
My new physics professor literally talks about nothing but his childhood and women during lecture halls. We seriously have taken half of a page of notes throughout this entire semester, and our book doesn't explain the content very well. I was wondering if any of you could help me out here, because even after talking to my professor, he still doesn't teach any relevant information. I would really appreciate your input for either this problem or what to do about this professor. He's the only one who teaches all of my physics classes until I'm a junior in college, and right now I haven't even finished my freshman semester... Suggestions?

Now that my rambling is complete, here's this homework problem:

Two waves of light in air, of wavelength [lambda]= 6.00 nm, are initially in phase. Each wave then travels through a different plastic layer, the thickness of layer 1 being L1=4.00 micrometers, and layer to being L2=3.50 micrometers. The indices of refraction are n1=1.40 and n2=1.60, respectively.

a) What multiple of lambda gives their phase difference after they both have emerged from
the layers?
b) If the waves later arrive at some common point with the same amplitude, is their
intereference fully constructive, fully destructive, intermediate but closer to fully
constructive, or intermediate but closer to fully destructive?