If one includes wave behaviors as part of this, I find students will have
trouble with the constancy of speed of waves as frequency changes. They will
apply the formula but when asked what happens to wavelength and speed when
frequencyt changes they will have trouble. It is a conceptual problem.
Again, I suspect that we don't build the same conceptual errors here that we
do in Mechanics as we do not kinestheticallt interact with waves and optics
as much as motion and force.