* Frequency (f): Frequency remains constant. This is because frequency represents the number of wave cycles passing a point per second, and this is determined by the source of the wave.
* Wavelength (λ): Wavelength changes. The speed of the wave changes as it enters a new medium, and since the relationship between speed (v), frequency (f), and wavelength (λ) is given by *v = fλ*, wavelength must adjust to accommodate the change in speed.
* Speed (v): Speed changes. The speed of a wave is determined by the properties of the medium it travels through. For example, light travels faster in air than in water.
* Amplitude (A): Amplitude can change, but it doesn't have to. The amount of energy transferred by the wave can be affected by the change in medium, leading to a change in amplitude. However, in some cases, the amplitude might remain relatively constant.
Therefore, the pair of characteristics that cannot change when a periodic wave travels from one medium to another is frequency (f) and the period (T).
Important Note: The period (T) is the time it takes for one complete wave cycle. It is the inverse of frequency (T = 1/f). Since frequency remains constant, the period also remains constant.
