prisms and doppler

[Bomikepa]

so different colors are the result of diff frequencies right? or is it diff wavelength or is it both?

and according to velocity= freq x wavelength,

we know that higher freq light ie blue light vs red has a smaller wavelength?

i have trouble understanding the dispersion? of light through a prism i just wanted to clarify that the higher freq. light bends more?

since the freq is constant and so is V that means that wavelength changes when it entered a diff medium like a prism?

but doesn't V change now because its going through a diff medium ( from air through glass)?

so if V does change, and F is constant then wavelength must change?

so the higher freq light like blue has a smaller wavelength and aslo bends more than lower energy light?

diffraction is when you have light go through some small slit
refraction is bending of light through a diff medium
what exactly is dispersion? i tend to confused the three

also with Doppler we dont have a TRUE change in freq correct, its just a PERCEIVED change in freq? the same follows with the wavelength right?


help please!

so lost lol

---

Members don't see this ad.

 

[rfvbnmju]

I'll tackle the parts I feel ok doing.

so different colors are the result of diff frequencies right? or is it diff wavelength or is it both?

we know that higher freq light ie blue light vs red has a smaller wavelength?

i have trouble understanding the dispersion? of light through a prism i just wanted to clarify that the higher freq. light bends more?

since the freq is constant and so is V that means that wavelength changes when it entered a diff medium like a prism?

but doesn't V change now because its going through a diff medium ( from air through glass)?

As light goes from one medium to another, the only thing that changes is velocity and wavelength. I remember this by thinking light doesn't gain or lose energy between mediums. From, E=hf , if E is constant and h is constant then f must be constant also.

so if V does change, and F is constant then wavelength must change?

Yep
velocity does drop according to c=nv; n is index of refraction

so the higher freq light like blue has a smaller wavelength and aslo bends more than lower energy light?

diffraction is when you have light go through some small slit
refraction is bending of light through a diff medium
what exactly is dispersion? i tend to confused the three

I'm going to quote a site for dispersion.

"In a dispersive material, different wavelengths travel at different speeds, which is the same as saying that each wavelength of EM Rad has a different refractive index in the material! The practical result of this is that no one path is the shortest for all wavelengths in most optical systems. Different wavelengths of EM Rad always follows their own fastest route though an optical system."
http://www.optics4kids.org/home/tutorials/dispersion.aspx

Basically, each wavelength of radiation by following their fastest route, takes a different path through the prism (this is the refraction) and exits at a different place. This accounts for the spreading of white light into the colors.

Red gets refracted the least while purple gets refracted the most.

also with Doppler we dont have a TRUE change in freq correct, its just a PERCEIVED change in freq? the same follows with the wavelength right?

Yep doppler is only a perceived change in freq b/c the waves are either being smashed together (if the obj is moving towards you) or spread apart (if obj is moving away)

 

[Bomikepa]

thanks!

so if we are every asked in a question about Doppler if the freq. or wavelength changes, the answer is they do not?

Would the question stem have to specifically state "what is the perceived change in freq" or what is the perceived change in wavelength in order for us to say that either the variables change?

also so basically each color has its own "unique" value of n so to speak when they all travel through the same prism, resulting in diff amounts of bending! thats kinda weird....so its not even depending on the material is passes then?

for ex if the light passed through plastic, each color would follow its own unique "n" and bend according to that instead of bending according the n value of the plastic?

 

[milski]

thanks!

so if we are every asked in a question about Doppler if the freq. or wavelength changes, the answer is they do not?

Would the question stem have to specifically state "what is the perceived change in freq" or what is the perceived change in wavelength in order for us to say that either the variables change?

also so basically each color has its own "unique" value of n so to speak when they all travel through the same prism, resulting in diff amounts of bending! thats kinda weird....so its not even depending on the material is passes then?

for ex if the light passed through plastic, each color would follow its own unique "n" and bend according to that instead of bending according the n value of the plastic?

The set of n-s is specific for the material. For some materials n is virtually the same for all frequencies, for some it varies more.

There is no preferred reference frame for observing frequencies. The change will depend on how the sender and receiver move. Neither of them is more real than the other. In other words, to talk about frequency, you have to define where are you measuring/observing it.

 

[Bomikepa]

so n is materia specific...ie prism glass but it can change in some instances for diff frequencies.

Following that, diff colors of light have diff frequencies right? but while the freq's are all diff they never change when light passes through the glass prism?

red light maintins its freq as it goes from air through the prism, same with blue light, but because they have diff frequencies ( but the same velocity) they bend differently because n in same cases n can vary with the frequency?

 

[milski]

so n is materia specific...ie prism glass but it can change in some instances for diff frequencies.

Following that, diff colors of light have diff frequencies right? but while the freq's are all diff they never change when light passes through the glass prism?

red light maintins its freq as it goes from air through the prism, same with blue light, but because they have diff frequencies ( but the same velocity) they bend differently because n in same cases n can vary with the frequency?

Yes to everything except same velocity. Different n correspond to different velocities.

Keep in mind that differences due to dispersion are very minimal. Unless you are dealing with high quality optics or explicitly interested in dispersion, you can ignore it.

It is on the list of topics for MCAT but there is not much you can be asked about it. Knowing what it is should be pretty much what you need to know.

 

[Bomikepa]

i geuss what i meant by same velocity is that for eg blue light and red light have the same velocity before they hit the prism, but once they ENTER the prism their velocities do change, along with the wavelength?