Memorize speed of sound & light?

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OK, guess I'll memorize them, thanks.

Understand that the velocity of light may change in a medium, but the speed of light is always a constant.
Are you sure about that? I could've sworn it went slower through glass and stuff.
 
Are you sure about that? I could've sworn it went slower through glass and stuff.

Read this post I made last week.

In short, the index of refraction is the ratio of the speed of light, which is a constant, and the effective velocity of light in a medium. When light passes through a medium, it doesn't travel in a straight line, hence the amount of time it takes for a photon to enter a medium and come out the other side is longer than it would take if it were traveling in a vacuum. It's not because it's traveling slower - the speed of light is a constant in all reference frames - it's because the path isn't straight, therefore the overall velocity is less than the speed of light.

This might seem like a superfluous distinction, but it isn't - a lot of misunderstandings are due to people thinking that light slows down in a medium. It tends to screw with their idea of frequency, wavelength, etc.
 
Read this post I made last week.

In short, the index of refraction is the ratio of the speed of light, which is a constant, and the effective velocity of light in a medium. When light passes through a medium, it doesn't travel in a straight line, hence the amount of time it takes for a photon to enter a medium and come out the other side is longer than it would take if it were traveling in a vacuum. It's not because it's traveling slower - the speed of light is a constant in all reference frames - it's because the path isn't straight, therefore the overall velocity is less than the speed of light.

This might seem like a superfluous distinction, but it isn't - a lot of misunderstandings are due to people thinking that light slows down in a medium. It tends to screw with their idea of frequency, wavelength, etc.

basically MD Odyssey is a stud (guy or girl?) and even though PS is my forte i'm constantly learning **** from him.

but MD Odyssey, let's say light goes though different mediums and is always entering perpendicularly. say for instance from glass to water or something. then both the velocity and speed decrease no? the time it takes to travel through the denser material is greater than the less dense material.
 
Let's say light goes though different mediums and is always entering perpendicularly. say for instance from glass to water or something. then both the velocity and speed decrease no? the time it takes to travel through the denser material is greater than the less dense material.

I appreciate the commendation, thanks.

Density isn't necessarily the best metric to use - in general, the velocity of an EM wave propagating through a material is dependent upon the wavelength. As an example, consider the case of glass. For visible light, glass is largely transparent. But for UV radiation, the absorption coefficient is rather large. Glass, for all intents and purposes, looks like concrete to UV radiation, which is why, in principle, one doesn't get a sunburn through glass.

My personal perspective is that, for visible, UV, and higher energy light, the simplest way to look at it is as discrete packets of energy. Lower frequency, RF sources are the only sorts of radiation that make any sense to me as waves. This is probably more or less a construct of the application. But at the end of the day, light is still a stream of photons. This approach also extends itself quite naturally to quantum mechanical world. As an example, consider the case of Young's double slit experiment. One can perform that experiment with an electron beam and get precisely the same type of result.
 
I appreciate the commendation, thanks.

Density isn't necessarily the best metric to use - in general, the velocity of an EM wave propagating through a material is dependent upon the wavelength. As an example, consider the case of glass. For visible light, glass is largely transparent. But for UV radiation, the absorption coefficient is rather large. Glass, for all intents and purposes, looks like concrete to UV radiation, which is why, in principle, one doesn't get a sunburn through glass.

My personal perspective is that, for visible, UV, and higher energy light, the simplest way to look at it is as discrete packets of energy. Lower frequency, RF sources are the only sorts of radiation that make any sense to me as waves. This is probably more or less a construct of the application. But at the end of the day, light is still a stream of photons. This approach also extends itself quite naturally to quantum mechanical world. As an example, consider the case of Young's double slit experiment. One can perform that experiment with an electron beam and get precisely the same type of result.

Okay, so I am going to quote EK before I ask my question:

"although the velocity of a wave is always given by the product of the wavelength and the frequency, the velocity is dictated by the medium through which the wave travels. A chance in frequency or wavelength does not change the velocity of a wave in a given nondispersive medium. Nor does the velocity of the wave source affect the velocity of the wave itself...."

Is the reason you say that the velocity of light is dependent on wavelength (and not the medium), because you are treating it as a particle and not a wave? For the MCAT, how should I look at light in order to answer questions?


thanks!
 
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