Answer
$4.4\times10^{26}\frac{photons}{s}$
Work Step by Step
The microwave oven’s power rating of 720 W is the energy output per second. Divide this power by the energy of one photon to find the number of photons produced per second.
Equation 27–4 gives us the energy of one photon.
$$E_{photon}=hf=\frac{hc}{\lambda}$$
Number per second = $\frac{P}{E_{photon}}=\frac{P \lambda}{hc}$
$$=\frac{(720W)(0.122m)}{(6.63\times10^{-34}J \cdot s)(3.00\times 10^8 m/s)}$$
$$=4.42\times10^{26}\frac{photons}{s}$$
