The minimum intensity of light to be detected by human eye is 10−10W/m2. The number of photons of wavelength 5.6×10−7mentering the eye, with pupil area 10−6m2, per second for vision will be nearly
A
100
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B
200
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C
300
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D
400
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Solution
The correct option is C 300 By using I=PA;where P = radiation power ⇒P=I×A⇒nhctλ=IA⇒nt=IAλhcHence number of photons entering per sec the eye (nt)=10−10×10−6×5.6×10−76.6×10−34×3×108=300.