how do you relate different terms in E=hf

[inaccensa]

---

Members don't see this ad.

I'm strictly looking at light

E= hf =hv/lambda

Now in chromatic dispersion, red light with the longest wavelength, smallest frequency and Energy *(which i completely understand) moves fast (dont follow the relation based on the equation)

E increases, wavelength decreases, shouldnt v and E be directly proportional?

 

[karafox]

I'm not sure what you mean, but:

E_photon = hf
E_photon = h(c/lambda)

c = speed of light, a constant (in a vacuum).

 

[inaccensa]

I'm not sure what you mean, but:

E_photon = hf
E_photon = h(c/lambda)

c = speed of light, a constant (in a vacuum).

yeah I'm asking how energy of a photon and velocity are related. I would think in direct proportion, but it doesnt seem so...Based on EK's explanation, I stated above

 

[costales]

yeah I'm asking how energy of a photon and velocity are related. I would think in direct proportion, but it doesnt seem so...Based on EK's explanation, I stated above

Photon energy is always proportional to frequency, no matter what. Photons travel at c until they enter a medium where they slow down by a factor n (index of refraction) which is defined as n = c/(speed in medium). The frequency doesn't change - it's the wavelength that changes to reduce the speed. For example, when blue light enters glass, it is still visible light even tho its wavelength in glass is "technically" in UV range.

 

[karafox]

If you're talking about a photon traveling in a vacuum, then velocity is the speed of light, c, which does not change.

Energy and the wavelength are inversely proportional, h and c are constants.

 

[inaccensa]

Photon energy is always proportional to frequency, no matter what. Photons travel at c until they enter a medium where they slow down by a factor n (index of refraction) which is defined as n = c/(speed in medium). The frequency doesn't change - it's the wavelength that changes to reduce the speed. For example, when blue light enters glass, it is still visible light even tho its wavelength in glass is "technically" in UV range.

wavelength increases and velocity decreases when light is refracted in a medium with higher "n" ???

In a prism, red light wavelength > violet light, and it has a greater velocity and bends less?

Arent these statements contradicting.

If Frequency is constant, one must increase and other decrease

 

[karafox]

[Incorrect]

 

[MT Headed]

.

 

[tn4596]

I am uncomfortable with this logic.

yea...that wrong
lets jsut say,for chromatic dispersion, a dispersive medium have different refective index for everytype of electromagnetic spectrum...so i guess that explain the red light traveling faster, because it might experiencing a lower refective index than say blue light. In this case, the decrease in wavelength cause a decrease in velocity. Frequency is constant.
velocity of light is dependent of refractive index of medium, c (the speed of light in vacuum is constant). Energy is dependent on frequency, so energy is constant also regardless of medium.

 

[karafox]

[Incorrect]

 

[tn4596]

What's uncomfortable about it?

a = bc
Suppose b is a constant and c is decreased by a factor of 2.
Therefore, a should be increased by a factor of 2 for the above to hold true.

no buddy... if c is decreased, then a will be decreased too...

 

[MT Headed]

I think we got off track with the following statement: 'wavelength increases and velocity decreases when light is refracted in a medium with higher "n" ???'

Wavelength decreases when the velocity decreases. E = h (v/lambda). E and h aren't changing in this scenario, just v and lambda.

 

[karafox]

Sorry guys, I was NOT thinking! Embarrassing. But yes, you are correct, it is a direct proportion. Again, sorry for the confusion.

Do you agree that red light has a smaller angle of refraction (when compared to blue light from vacuum to a prism), and thus a greater phase velocity?

You can deduce that n_red < n_blue.
v_red = c/n_red > v_blue = c/n_blue.

Where,

v = phase velocity of a wave through a prism
c = speed of light through a vacuum
n = refractive index of a certain light of the prism.

[E_photon = energy of a photon => when treating for a particle of light, not a wave.]