Hi there, quick question about units. I know wavenumber can be defined as 1/λ or 2π/λ, the latter sometimes being termed 'angular' wavenumber. Is there an agreed upon way of distinguishing between these two definitions when displaying units on, for example, a graph or paper? I've seen units such as (m-1) which is ambiguous or (cpm) which I presume to mean cycles per metre and thus refer to angular version, but also (rad m-1). Is there a standard that should be followed? Or is it a free for all? Cheers, Jesse
It's a bit of a free for all. You can often tell by context, but sometimes it's quite confusing. E.g., if waves are referred to as ##\cos kx,## then ##k = 2\pi / \lambda## (radians/m). Using cpm (analogous to Hz = cps) whenever you mean cycles, not radians, is a good habit. If you are working with both wave number and frequency, you definitely want to stick to the same convention for both.
I think which one you like to use is probably dependent on the field you are working in. In physics, because we almost always express waves like ##\cos(kx)## or ##e^{ikx}##, we almost always use angular wave number, and ##1/\lambda## is very very rarely used.