There is a question on a test which goes like this:
"Given two electromagnetic waves, one of wavelength 6.0 X 10-7 m and the other of wavelength 7.0 X 10-7 m, travelling in space. When the two waves meet in space, they combine (interfere) to form a wavelength of _______"
The answer is "none, they do not interfere."
My guess was that the wavelength would be the LCM of the two wavelengths, but it seems that I am wrong. Could someone explain this to me?
I doubt the question is trying to test knowledge of a distinction between photons interfering and their probabilistic wave functions interfering as we haven't learned that yet, although it is possible.