wave speed
Yes, this can be very complicated. But what should a middle-school student understand about light? You see stuff in textbooks that is either wrong or just a bunch of disconnected factoids (I like the word factoid). So, what do I think is important about light (not at the Maxwell's equations level)
What is a wave
If you want to talk about light, you need to talk about waves. So what is a wave? I like to start with an example. Suppose you are in a sports stadium - maybe a football game. Some inspired fan decides to start a wave. If you look at the individual people, the wave might be…