Changes in Light and Sound Properties

[avalonisland888]

According to UWorld, when a wave moves from one medium to another, its frequency does not change. But how come the frequency changes based on the Doppler Effect if the medium remains the same? What exactly about a sound wave changes from one medium to another - speed and wavelength? What about light? I'm thinking the light's frequency does not change because then the colour will change, but the speed and wavelength can change depending on the medium?

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[JimKimSlim]

Doppler effect changes the frequency because the source of sound or the receiver is moving. When a sound wave is traveling from one medium to another, its wavelength changes and hence the velocity of the wave but not the frequency. Similarly, light’s frequency does not change but its wavelength does. If you have a laser and shoot it to a glass of water, it will retain its color and hence frequency. However, the wavelength decreases because water particles are denser than air particles and blocks the propagation of light over distance, hence reducing the velocity of the light. Same thing happens in the ocean, where the light’s velocity reduces to zero at certain depth, aka the midnight zone.

 

[avalonisland888]

Doppler effect changes the frequency because the source of sound or the receiver is moving. When a sound wave is traveling from one medium to another, its wavelength changes and hence the velocity of the wave but not the frequency. Similarly, light’s frequency does not change but its wavelength does. If you have a laser and shoot it to a glass of water, it will retain its color and hence frequency. However, the wavelength decreases because water particles are denser than air particles and blocks the propagation of light over distance, hence reducing the velocity of the light. Same thing happens in the ocean, where the light’s velocity reduces to zero at certain depth, aka the midnight zone.

Ah I understand now. Thank you!