The photochemistry of vision is best understood as a sequence of biochemical eve

Question

The photochemistry of vision is best understood as a sequence of biochemical events beginning with an isomerization of all-trans-retinal to 11-cis-retinal upon photon absorption. The flux of visible photons reaching Earth from the North Star is about 4x103 mm-2s-1. Of these photons, 30% are absorbed or scattered by the atmosphere and 25% of the remaining photons are scattered by the cornea surface. A further 9% are absorbed inside the cornea. The area of the human pupil is about 40 mm2 and the response time of the eye is about 100 ms. Of the photons passing through the pupil, 43% are absorbed in the ocular medium (the vitreous humor.) How many photons from the North Star are focused onto the retina in 100 ms?

Explanation / Answer

photon flux= number of photon per unit area per unit area=4*10^3 =4000 mm^-2sec^-1

absorbed by atmosphere= 30 percent=1200

left =2800

scaterred by cornea= 25 percent of remaining =700

left=2100

absorbed inside cornea=9 percen=189

left=1911

absorbed in ocular medium=43 percent =821.73

left =focussed onto retina=1089.27

number of photon focussed=1089.27*40*100*10^(-3)=4357 (approx)

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