Which of the following wave characteristics remain unchanged when a wave crosses a boundary

Question

Which of the following wave characteristics remain unchanged when a wave crosses a boundary into a different medium? (Select all that apply.)

__velocity

__amplitude

__frequency

__wavelength

__direction

Answer 1

Not velocity; the index of refraction is a measure of how much light is slowed when traveling through a given medium.

Not amplitude; the boundary is likely to reflect some of the light rather than let the whole amount into the second medium.

Frequency is one answer.  This does not change unless the wave goes through a medium with a nonlinear transfer function.  Elementary optics classes don't usually get into things like nonlinear media.

If velocity changes but frequency does not, then wavelength will also necessarily change in proportion to the velocity.  This isn't the answer either.

Snell's Law gives the rule for calculating the new direction of propagation when a material crosses to a different medium.  If the direction didn't change, we wouldn't need Snell's Law.  This isn't the answer either.

Of these, only frequency will remain unchanged.

Answer 2

only the frequency because it depends on the source of the wave