(6pts) Can You See a Single Photon? T he wavelength corresponding to the maximum
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Question
(6pts) Can You See a Single Photon? The wavelength corresponding to the maximum sensitivity
of the human eye is 510 nm, the limit of sensitivity of the dark-adapted eye has been shown to be correspond to
a 100 ms flash of light of total energy 240 eV. (Little Shop of Physics- Colorado State University)
1 J = 6.241509 x 1018 eV
a) What is the energy of a single photon at this wavelength?
b) How many photons does the flash contain?
c) If 60% of the incident light is lost to reflection and absorption by tissues of the eye, determine how many photons reach the retina and if you can see a single photon?
Explanation / Answer
a) Wavelength = 510nm = 510×10^-9m
wavelength = speed of light / frequency
frequency = speed of light / wavelength
= 2.99×10^8(m/s)/510 ×10^-9m
= 5.86×10^14s^-1
Energy = hv
h = planck constant , 6.626×10^-34J.s
v = frequency
Therefore,
E = 6.626×10^-34J.s × 5.86×10^14s^-1
= 3.88×10^-19J
b) Energy of flash = 240eV
1eV= 1.602×10^-19J
240eV = 240×1.602×10^-19J = 3.84×10^-17J
No of poton = 3.84×10^-17J/3.88×10^-19J
= 99photons
c) (60/100) × 99photons = 59photons
Therefore,
not possible to see single photon
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