Chapter 31 - Atomic Physics - Problems and Conceptual Exercises - Page 1115: 90

(D) $Power=7.16W$

We know that $Power=n\frac{hc}{\lambda}$ We plug in the known values to obtain: $Power=\frac{(1.49\times 10^{19}photons/s)(6.63\times 10^{-34}J.s)(3\times 10^8m/s)}{414\times 10^{-9}m}$ $Power=7.16W$ Thus, option (D) is correct.