A longitudinal wave passes into a new medium in which it travels faster. What happens to its frequency?

1. The frequency of a longitudinal wave is set by the vibrations of whatever created it. 2. Those vibrations are not altered by the wave entering a new medium. 3. The frequency is therefore always unchanged, irrespective of any changes in speed. 4. Because the period is the inverse of the frequency, the period stays the same as well. 5. Assuming a faster wave must have a higher frequency is the trap here. 6. It is the wavelength, not the frequency, that adjusts when the speed changes. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 9: Longitudinal waves_