Question the human eye can barely detect a star whose, Ask an Expert

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Question: The human eye can barely detect a star whose intensity at the earth's surface is 1.8 x 10^-11 W/m². If the dark adapted eye has a pupil diameter of 6.5 mm,

Part A: How many photons per second enter the eye from the star?

I need help to solve the above question and assume the starlight has a wavelength of 550 nm.

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