1. The problem statement, all variables and given/known data (a)Estimate the number of photons per second emitted by a 100-W lightbulb, assuming a photon wavelength of 550nm.(b) A person can just see this bulb for a distance of 800m, with the pupil dilated to 7.5mm. How many photons per second are entering the pupil? 2. Relevant equations E=hc/λ h=6.63*10^-34 J s c=3.0*10^8 m/s 1eV=1.602*10^-19 J 1 watt second = 100 joules 3. The attempt at a solution For part (a) E=hc/λ=(6.63*10^-34 J s * 3.0*10^8 m/s)/(550nm) =3.616*10^-19 J convert to eV: (3.616*10^-19 J * (1eV/1.602*10^-19J)=2.257 eV per photon 100 watt sec = 100 joules (100 joules * (1eV/1.602*10^-19J))/2.257eV) = 2.77*10^20 photons For part (b): Not excatly sure how to proceed. I made a circle and determined the percent of the circumference was the 7.5mm pupil then multiplied that by the total number of photons, but the answer I got did not mach the book. C=pi*d=pi*1600m=5026.548m (7.5mm/5026.548m)*2.77*10^20 photons = 4.13*10^14 photons. The answer in the book is 6.1*10^9 photons. How can I get to this answer?