Refraction.

[MedPR]

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Why is D wrong? It's true, just not the correct answer for the question right?

 

[milski]

Right, it is correct but does not answer the question.

 

[MedPR]

Right, it is correct but does not answer the question.

Ok thanks. I'm glad I wasn't confused!

 

[SaintJude]

How is that light of longer wavelength (with lower frequencies) will actually move faster through a medium than light of higher frequencies?

 

[MedPR]

How is that light of longer wavelength (with lower frequencies) will actually move faster through a medium than light of higher frequencies?

v=f*lambda. frequency doesn't change, so bigger lambda (longer wavelength) = faster wave. At least that's what I told myself...

 

[SaintJude]

That works perfectly for me and even allows me to remember why red colored-light "sees" a lower index of refraction than violet, an will thus bend less than violet. I don't even care if it's an oversimplification. This works.

 

[pfaction]

v=f*lambda. frequency doesn't change, so bigger lambda (longer wavelength) = faster wave. At least that's what I told myself...

Huh? The frequency here does change. TPR says that dispersion is an exception: violet has a higher indices of refraction than red, because it has a higher frequency. It has a smaller wavelength.

Here is what TPR says:
When light moves from one medium to another, some wavelengths are bent more than others - EM waves of different frequencies travel slightly different speeds through different mediums. When light travels through a medium, different frequencies have different speeds. In general, the higher the frequency of the light, the slower the speed. The greater the index of refraction, the more the light will be bent on entering the medium, so high frequency light will bend more than red light.

 

[MedPR]

Huh? The frequency here does change. TPR says that dispersion is an exception: violet has a higher indices of refraction than red, because it has a higher frequency. It has a smaller wavelength.

Here is what TPR says:
When light moves from one medium to another, some wavelengths are bent more than others - EM waves of different frequencies travel slightly different speeds through different mediums. When light travels through a medium, different frequencies have different speeds. In general, the higher the frequency of the light, the slower the speed. The greater the index of refraction, the more the light will be bent on entering the medium, so high frequency light will bend more than red light.

I don't see anything in there that says frequency changes. It is comparing high frequency light (violet) with low frequency light (red). It isn't saying anything about either light changing frequency.

 

[pfaction]

I don't see anything in there that says frequency changes. It is comparing high frequency light (violet) with low frequency light (red). It isn't saying anything about either light changing frequency.

Sorry, I meant that since the frequencies are different, with light as the exception, the speed changes. I guess v=flamda works over all though. I'm re-reading the chapter right now to make sure I don't say anything stupid.

 

[MedPR]

Sorry, I meant that since the frequencies are different, with light as the exception, the speed changes. I guess v=flamda works over all though. I'm re-reading the chapter right now to make sure I don't say anything stupid.

Yea, I didn't say the speed didn't change, I said the frequency doesn't change. The speed of any wave will change when it changes mediums.. Light is not an exception there.

If the wave goes from a low n medium to a high n medium, it will slow down. In order to obey the v=f*lambda equation, lambda must also go down. So lower wavelength travels slower than higher wavelength.

 

[SaintJude]

I think that the Energy per photon between violent light and red light is the same. E = hc/lambda = hf.

Thus to compensate, violet has the largest frequency and thus the smallest wavelength. Red has the smallest frequency and thus the largest wavelength.

Edit: Oh nevermind, you guys are talking about something else--about frequency staying constant between media...Oops, sorry!

 

[Laurac]

Why is D wrong? It's true, just not the correct answer for the question right?

 

[Laurac]

Higher freq=shorter wavelength =more energy--->Greater deflection in direction/speed, so the red end of light comes out of the thinner end of the prism. Think about it: short wavelength (gamma and X Rays ) kill. Visible light and radio waves don't (unless you are putting your head in a microwave oven ) low frequency electromagnetic waves (like a ham radio) move slow enough that you can sometimes hear an echo of your transmission a few seconds after you transmit as the radio wave circles the globe!! "D" is wrong because optical material is not going to change the wavelength. Only materials with fluorescent properties will.

 

[aalamruad]

Higher freq=shorter wavelength =more energy--->Greater deflection in direction/speed, so the red end of light comes out of the thinner end of the prism. Think about it: short wavelength (gamma and X Rays ) kill. Visible light and radio waves don't (unless you are putting your head in a microwave oven ) low frequency electromagnetic waves (like a ham radio) move slow enough that you can sometimes hear an echo of your transmission a few seconds after you transmit as the radio wave circles the globe!! "D" is wrong because optical material is not going to change the wavelength. Only materials with fluorescent properties will.

I'm pretty sure that the prism does actually change the wavelength of the light. Since frequency is a source variable, vavelength is the only thing that can change, and since light slows down upon entering the prism, its wavelength must be decreasing, right? I'm confused as to why D is incorrect too (I understand why C is correct)

 

[aldol16]

Frequency cannot change. Otherwise, you would have a buildup of waves at the interface, which would destroy the interface in a matter of seconds. There have been many posts about this before and this is a common source of confusion.

 

[aalamruad]

Frequency cannot change. Otherwise, you would have a buildup of waves at the interface, which would destroy the interface in a matter of seconds. There have been many posts about this before and this is a common source of confusion.

Right, so what's wrong with choice D?

Edit: Never mind, just realized that D is correct but it just doesn't answer the question.