Answer
a) 3.18 $\times 10^{15}$ photons per second
b) 4.7 $ \times 10^{14}$ Hz
Work Step by Step
(a) We know that
$\frac{n}{t}=\frac{P\lambda}{hc}$
We plug in the known values to obtain:
$\frac{n}{t}=\frac{(1.0\times 10^{-3}W)(632.8\times 10^{-9}m)}{(6.63\times 10^{-34}J.s)(3\times 10^8m/s)}$
$\frac{n}{t}=3.18\times photons/s$
(b) We can find the required frequency as follows:
$f=\frac{c}{\lambda}$
We plug in the known values to obtain:
$f=\frac{3\times 10^8m/s}{632.8\times 10^{-9}m}$
$f=4.7\times 10^{14}Hz$
