# Two waves of light in air travel through a layer

1. Dec 18, 2016

### Any Help

1. The problem statement, all variables and given/known data

Two waves of light in air, of wavelength 550 nm, are initially in phase. They then both travel through a layer of plastic as shown in the figure, with L1 = 4.00 μm, n1 = 1.40, L2 = 3.50 μm , and n2 = 1.60. What is their phase difference after they both have emerged from the layers, when they arrive at the same point?

2. Relevant equations
N is the numbers of lemdas
N1=L1*n1/λ
N2=L2*n2/λ
N in air = (L1-L2)/λ n(air)=1

3. The attempt at a solution
N2+Nair-N2=0.909 but the correct answer is 5.71?????

2. Dec 18, 2016

### TSny

"Phase difference" is an angle (in radians), not the number of λ's.

3. Dec 18, 2016

### Any Help

What is the name of the difference in wavelengths?

4. Dec 18, 2016

### TSny

You could also call the difference in wavelengths the "phase difference". So, the answer of .909 wavelengths is a correct answer. However, does the answer of 5.71 include any units?

5. Dec 18, 2016

### Any Help

no only number

6. Dec 18, 2016