Frequency of sound wave created vs. Frequency of sound wave crossing medium

[Lostintime]

I was wondering why this happens in sound waves.

You use a certain amount of energy X in order to create waves 1 and 2.
Wave 1 is created in a medium with lighter molecules. It has a higher frequency and higher velocity.
Wave 2 is created in a medium with heavier molecules. It has a lower frequency and a lower velocity.


Now wave 2 crosses from its medium into the medium of wave 1. Its velocity now increases, along with its wavelength, but its frequency stays the same.

Energy 1=Energy 2
v1=v2
But f1>f2
while &#955;1<&#955;2

I was wondering if this scenario was correct, how two different waves of same velocity but different f and &#955; were generated simply by their origins.
Also, what exactly is the reason that f remains constant when a wave crosses a medium, while its velocity increases?

How does this compare to EM Waves?

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[Trauma16]

Sound waves are special because they are longitudinal waves, rather than transverse waves. Because of this, the wave's velocity is highly dependent on how close the atoms are to each other in the medium. Each atom must pass the energy of the wave to the next in the medium, so the closer they are to each other the faster they can do this (the speed that the molecules can pass the energy along is known as elasticity). This causes the sound wave to travel faster in denser media (such as water, or iron, where the velocity of sound is 1500 m/s and 5000 m/s, respectively). However, two aspects of the medium affect the velocity of the wave: elasticity and inertia. The heavier molecules of the second medium resist change more than the first medium, resulting in a slower wave. Since the molecules are heavier, their movement at a slower speed has the same energy as the faster movement of the atoms of the other medium with a lower mass.

The frequency doesn't change because frequency is directly related to energy (E = hf), and energy is conserved. The main difference between sound and EM waves is the fact that EM waves are transverse, so the medium is displaced perpendicularly to the direction of motion. This means that the inertia of the media is more important to the speed of the wave than the elasticity (because now, elasticity can't help to move the wave along, like in longitudinal waves). Thus, when an EM wave meets a heavier medium, it will slow down (like in water).

 

[Lostintime]

Thank you, i dont believe my first question was answered yet though.

Is the scenario correct??

 

[Trauma16]

When the wave crosses into the other medium, its frequency must stay the same to conserve energy. Energy 1 = Energy 2 by conservation of energy, but v1 does not equal v2. Since the frequency is dictated by the medium in which the wave was created, it does not change when transitioning to other media, so f1 = f2. Since v= f&#955; and the velocity increases when the wave goes into medium 1, the wavelength must increase as well. Thus, f1 = f2, v1 > v2, &#955;1 > &#955;2.

For waves, just know that the initial frequency is dependent on the medium in which the wave is created. When the wave goes to different media, the frequency must stay the same, meaning that the changes caused by the medium only affect wavelength and velocity.