Problem 26.109 IP A film of oil, with an index of refraction of 1.40 and a thick

Question

Problem 26.109 IP A film of oil, with an index of refraction of 1.40 and a thickness of 1.60 cm , floats on a pool of water, as shown in the figure. (Figure 1) A beam of light is incident on the oil at an angle of 60.0 to the vertical.

Part A

Find the angle the light beam makes with the vertical as it travels through the water.

Part B

How does your answer to part A depend on the thickness of the oil film? (pick one answer)

decreases with increase of the thickness of the oil film increases with increase of the thickness of the oil film The answer to part A does not depend upon the thickness of the oil film.

Explanation / Answer

A. Using snell's law

for Air-oil interface

na*sin A1 = no*sin A2

for oil-water surface

no*sin A2 = nw*sin A3

using both equation

na*sin A1 = nw*sin A3

na = 1.00

nw = 1.33

A1 = 60 deg

A3 = arcsin (na*sin A1/nw)

A3 = arcsin (1*(sin 60 deg)/1.33)

A3 = 40.63 deg

B.

The answer to part (a) does not depend upon the thickness of the oil film, because theta depends only upon the original angle of incidence and the indices of refraction of air and water

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