I'm a high school physics teacher and this was a question posed to my Honors Physics class. [Simplified] A light wave travels from water to air. Which of the following variables does NOT change between the mediums?" A. speed B. wavelength C. amplitude D. frequency I intended the answer to be frequency. But, upon further analysis, I couldn't give a good answer as to whether the amplitude changes or not. I was thinking in terms of classical waves (e.g. strings, sound, water). But, I specifically used a light wave. In perusing PF, I saw a previous thread discussing whether light as a photon has an amplitude. I'll admit the discussion got really deep, but the conclusion seemed to be that amplitude doesn't quite apply to a single photon, and for a light "wave", intensity would be a better descriptor. However, I did say amplitude. The students know about energy/intensity vs. amplitude, but not really about light being wave and particle. They may be familiar with the concept though. My question is whether option C was ambiguous enough to warrant accepting it as an answer.