A predatory Angler Fish has evolved bioluminescence, so that it can make its own

Question

A predatory Angler Fish has evolved bioluminescence, so that it can make its own light of 600 nm wavelength that it uses like a flashlight to help it see. A species of jellyfish lives in deep ocean water (so that the only light that reaches it is the light produced by the angler fish). The body of the jellyfish is mostly water surrounded by a "thin film" of transparent cells with an index of refraction n_cells = 1.50. What is the minimum thickness of the layer of transparent cells that would produce constructive interference of reflected light? What is the minimum thickness of the layer of transparent cells that would produce destructive interference of reflected light? Why would evolution tend to favor jellyfish that have a layer of these transparent cells with the thickness that you found in part (b)instead of the thickness that you found in part (a)?

Explanation / Answer

Given data

the path difference = 2t

t = thickness of the cell

L' = wavelength of light in cell = L/ncell

L = wavength of light in water

(a)

In this the
for constructive interference 2t = mL/n

m = 1 , 2, 3, 4,5 ,6 ,7 .........

Put the value .....

2*t = 1*600*10^-9/(1.5)

t = 200 nm , 400 nm , 600nm , 800 nm, 1000 nm 1200 nm 1400 nm

tmin = 200 nm

(b)

for destructive interference 2t = L'/2 = mL/2n

for m = 1

Put the value ....

2*t = 600*10^-9/(2*1.5)

t = 100 nm

m = 3 , 5 , 7, 9

t = 300 nm , 500 nm 700 nm , 900 nm 1100 nm 1300 nm , 1500 nm 1700 nm

tmin = 300 nm

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