I was very pleased to see Josu Martinez-Perdiguero’s article in the November 2019 issue.1 Its arrival was well timed as I had literally just finished my lecture on the photoelectric effect. The analysis was spot-on in stressing the difference between the “bang-for-the-buck” that each photon packs (as measured by its frequency) vs. the number of photons in a beam (as measured by the intensity). However, I prefer a different approach compared to the I-V curve (Figs. 2 and 3). I posed the following question to my students on a quiz supporting the photoelectric effect lecture.

The guided conversation (usually with a dollar’s worth of quarters and dimes to represent equal intensities of blue and red photons) that follows goes a long way to drive home the point Martinez-Perdiguero was at pains to make.

AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.