I just noticed that we tend to call EM wavelengths shorter than

[jacket250]

I just noticed that we tend to call EM wavelengths shorter than visible light "rays" while we call we call those that are longer "waves". Why is that? Did we ever think that "rays" and "waves" were physically different?

 

[Studiot]

Hello jacket 250 and welcome to Physics Forums.

Actually there is a difference, not between the infra and ultra EM, but between the terminology.

Perhaps you have heard the term 'line of sight'?
Well rays refer to this aspect of EM radiation. The idea that light travels in straight lines and that you can draw a straight line path between the source and observer. The whole of geometrical optics in fact.

Radio, on the other hand, 'spreads out' and transhorizon reception has long been used.
Only when we started using microwave frequencies, closer to those of light, did we start using line of sight radio.

go well