The diagram shows light incident from above on a film of thickness d. Each of th
ID: 1648833 • Letter: T
Question
The diagram shows light incident from above on a film of thickness d. Each of the three materials in the figure can be chosen to be air, with index of refraction n=1.00, water, with index n=1.33, or glass, with index n=1.50. Under which of the following conditions will the reflected light be completely or nearly eliminated by interference?
(lambda2 refers to the wavelength of the light inside the thin film.)
(Note: In the case that d<<lambda2, you can assume the thickness is so small that the travel distance in material 2 has negligible affect on the phase of the wave. Treat this as if the two interfaces are almost right on top of each other.)
d<<lambda2, material 1 is air, 2 is glass, 3 is air.
d=lambda2/4, material 1 is glass, 2 is air, 3 is water.
d=lambda2/4, material 1 is air, 2 is water, 3 is glass.
d=lambda2/2, material 1 is glass, 2 is water, 3 is glass.
d=lambda2/4, material 1 is water, 2 is glass, 3 is air.
Explanation / Answer
Answer : (1) d=lambda2/4, material 1 is air(n=1.00), 2 is water, 3 is glass.
This is true because there would be 2 phase reversals, first between air and water and the other between water and glass. So the wavelength would be exactly in phase which means it needs to have PLD of (1/2) d=2/4 (2/4) = (1/2) (2/4)= (1/2) (1/2)= (1/2)