A laboratory dish, 30 cm in diameter, is half filled with a glucose/water soluti

Question

A laboratory dish, 30 cm in diameter, is half filled with a glucose/water solution. One at a time, 0.40 L drops of oil from a micropipette are dropped onto the surface of the solution, where they spread out into a uniform thin film. As more drops are added, the intensity of 600 nm light reflected from the surface decreases. The intensity reaches a minimum after a total of 13 drops have been added. In all questions, assume that the oil's index of refraction is smaller than the glucose/water solution's index.

What is the index of refraction of the oil?     

Explanation / Answer

total volume of drops

V = 0.4x13x 10^-9 m^3 = 5.2 x 10^-9 m^3

A = pi x 0.15x0.15 = 0.07 m^2

thickness of oil

t = V/A = 73.5649 nm

we know that for minimum intensity

2nt = wavelength /2

n = 2.039

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