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

(a) $1.74\times 10^{18}~photons$ (b) $1.74\times 10^{26}~photons/s$
(a) We can find the energy of each photon: $E = \frac{h~c}{\lambda}$ $E = \frac{(6.626\times 10^{-34}~J~s)(3.0\times 10^8~m/s)}{690\times 10^{-9}~m}$ $E = 2.88\times 10^{-19}~J$ We can find the number of photons emitted in each pulse: $\frac{0.500~J}{2.88\times 10^{-19}~J} = 1.74\times 10^{18}~photons$ (b) We can find the rate of photon emission: $R = \frac{1.74\times 10^{18}~photons}{10\times 10^{-9}~s}$ $R = 1.74\times 10^{26}~photons/s$