Q.

The minimum light intensity that can be perceived by the eye is about 10-10 W /m2 .The number of photons of wavelength5.6 x10-7 m that must enter the pupil of are 10-6m2 per sec for vision is approximately (use h =6.6x10-34 Joule -sec)

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a

3x102 photons

b

3x103 photons

c

3 x104 photons

d

3 x 105 photons

answer is A.

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Detailed Solution

Given that I=10−10W/m2=10−10Js−1m−2 Let the number of photons required be n. Then nhv10−6=10−10  or  n=10−6×10−10hv or  n=10−16λhc =10−16×5⋅6×10−76⋅62×10−343×108=3×102 photons
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