Answer
(a) $1.5\times 10^{20}photons/s$
(b) $1.0\times 10^{12}photons/s$
Work Step by Step
(a) We can find the number of photons per second as
$n=\frac{P\lambda}{hc}$
We plug in the known values to obtain:
$n=\frac{(45W)(650\times 10^{-9m})}{(6.63\times 10^{-34}J.s)(3\times 10^8m/s)}$
$n=1.5\times 10^{20}photons/s$
(b) We can find the number of photons per second as
$n=(1.5\times 10^{20})(\frac{\pi (\frac{5\times 10^{-3}m}{2})^2}{2827.4m^2})$
$n=1.0\times 10^{12}photons/s$
