Exploring Quantum Physics - Week 5 Question 3

Question:

How many photons is required to excite a hydrogen atom for the following lasers?

Red R: 650 nm
Green G: 532 nm
Violet V: 405 nm

Solution:

We need to have $0.99R_\infty hc = E \le \frac{nhc}{\lambda}$, therefore $n \ge  \frac{0.99R_\infty hc \lambda}{hc} = 0.99R_\infty \lambda$.

Plugging the values in, we have minimum n = 8, 6, 5 respectively.