Why frequency of sound wave does not change when moving from one medium to another ?
Well basically, the frequency relies only on the source which is making the wave. It doesn’t get affected by the medium like the velocity does. An example is when you make transverse waves along a rope, which has 2 sections – one is heavier than the other. The media are different, but the frequency must stay the same because the media is continuous – the end of one section of cord is physically tied to the other section of cord. If the end of the first section of cord is vibrating up and down with a given frequency, then since it is attached to the other section of cord, the other section must vibrate at the same frequency. If the two pieces of cord did not move at the same frequency, they would not stay connected, and then the waves would not pass from one section to another.
