Why don't frequency and period change when a wave refracts?

[Bashyboy]

Hi,

Okay, to my understanding refraction of a wave occurs when a certain wave passes through two different mediums that vary in density, causing the wavelength of that certain wave to change--whether it elongates or shrinks. So am I misunderstanding something? Also, in my textbook it asserts that frequency and period do not change as a result refraction, how is that so?

 

[Drakkith]

From wikipedia: Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another at any angle other than 90° or 0°. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth.

As for the frequency staying the same, imagine this. I go and I knock on your front door 10 times in 5 seconds. So the frequency of the maximum amplitude of the sound waves produced is 2 Hz. As I am knocking the waves travel through the door and from there out into the air to finally be heard by you. When the wave travels through the door and hits the boundary to the air it creates a wave in the air. How many times a second is the wave from the door causing a wave in the air? Two times per second. So the frequency has remained the same even though the length of the wave changed. (Which is how far the wave has propagated between my knocks.)

Look here: http://en.wikipedia.org/wiki/File:Wave_refraction.gif

As you can see, the waves on the left are traveling faster than the ones on the right. But look closely, each time a wave begins to hit the boundary it creates a new wave on the right. This wave stays synced to the original wave at the boundary while it is being created even though it is moving slower. If you count the number of waves created in 10 seconds at the boundary and compare it to the number of waves entering on the left and exiting on the right in 10 seconds all 3 will be the same.

 

[Bashyboy]

Okay, I understand now. Thank you.