## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

$N = 3.32\times 10^{14}~photons$
We can find the energy of each photon: $E = \frac{h~c}{\lambda}$ $E = \frac{(6.626\times 10^{-34}~J~s)(3.0\times 10^8~m/s)}{550\times 10^{-9}~m}$ $E = 3.614\times 10^{-19}~J$ We can find the number of photons emitted in each flash: $N = \frac{P~\Delta t}{E}$ $N = \frac{(0.0012~W)(0.100~s)}{3.614\times 10^{-19}~J}$ $N = 3.32\times 10^{14}~photons$