[lyner]

That's nicely put.
'The Hydrogen Atom' model which we all get taught is all too often used out of context and the Energy Levels in solids are much more complicated.
The quotation doesn't deal with the behaviour of light passing through a gas, though. Gases have very low refractive indices but the effect is still very broad band (except at absorption peaks). I wonder how that can be explained, in similar sorts of terms; it can't be due to mechanical vibrations - can it?

Having said that, the effect of em waves through ionised media can be treated as forced oscillations of the free electrons in a classical way.

[Bikerman]

Yes, that beats my (oversimplified) attempt at an explanation hands down  []

[labview1958 (OP)]

When light passes through a glass prism it breaks down to it's rainbow colours. Why when light passes through  a glass block, it does not break down to it's rainbow colours?

[lightarrow]

When light passes through a glass prism it breaks down to it's rainbow colours. Why when light passes through  a glass block, it does not break down to it's rainbow colours?

Because light passing through a prism is forced to refract in the same direction when it enters and when it escapes; passing through a glass block no: it is refracted in a direction when it enters and refracted in the opposite direction when it escapes, so the total refraction is zero.

[lyner]

You can get chromatic aberration, though - the blue 'ray' is shifted laterally a bit more than the red.

[lightarrow]

You can get chromatic aberration, though - the blue 'ray' is shifted laterally a bit more than the red.

That's true. Given the angle of incidence, the shift is proportional to the glass' thickness.

[labview1958 (OP)]

Does the refractive index of glass varies with the frequency of light?

[lightarrow]

Does the refractive index of glass varies with the frequency of light?

Of course, otherwise you wouldn't have dispersion (= separation) of colours with glass.

There are types of glass or other materials where the dispersion is lower, but there is always. A material with very low dispersion is CaF₂ (calcium fluoride) in the crystal form of fluorite; for this reason it's used in good, but expensive, optical instruments as high quality camera's lenses or telescopes' objectives (to have almost no chromatic aberration). Such materials are called apochromatic.
http://www.daviddarling.info/encyclopedia/A/apochromatic.html
http://en.wikipedia.org/wiki/Apochromat

[labview1958 (OP)]

Does it mean red light travels faster than blue light in glass? Is there any material where blue light travels faster than red light?

[lightarrow]

Does it mean red light travels faster than blue light in glass?

Of course.

Is there any material where blue light travels faster than red light?

In the right-side of the anomalous refraction curve of any substance (that is, on the right of the absorption band): wavelenght on the orizontal axis, index of refraction on the vertical axis.
See "anomalous refraction" or "anomalous dispersion".

[labview1958 (OP)]

If I shine a light on the moon, would the red light reach the moon a nanosecond earlier than the blue light.

[lightarrow]

If I shine a light on the moon, would the red light reach the moon a nanosecond earlier than the blue light.

Yes, if you shine the red light a nanosecond earlier than the blue... []
They arrive simultaneously. Why do you think they could arrive at different times?

[syhprum]

This assumes that the Earth Moon path is a pure vacuum which of course it is not.
The red and blue light has to pass Thru both the atmosphere and the ionosphere and a differential delay could well arise.

[lightarrow]

This assumes that the Earth Moon path is a pure vacuum which of course it is not.
The red and blue light has to pass Thru both the atmosphere and the ionosphere and a differential delay could well arise.

Correct. I assumed labview1958 intended to talk about a travel in the void, considering Earth's gravitational field.

[labview1958 (OP)]

As the moon is moving towards/away from earth, a light from earth would show a nanosecond blue/red shift. This is due to Doppler effect. Agree?

[lightarrow]

As the moon is moving towards/away from earth, a light from earth would show a nanosecond blue/red shift. This is due to Doppler effect. Agree?

If you are on the Moon observing a light beam from Earth, you will see it blue shifted if the Moon approaches Earth and red shifted if the Moon recedes from Earth.

[labview1958 (OP)]

Is it possible to design a "prism" in such a way that blue light is transmitted out while red light is internally reflected.

[Bored chemist]

As the moon is moving towards/away from earth, a light from earth would show a nanosecond blue/red shift. This is due to Doppler effect. Agree?

If you are on the Moon observing a light beam from Earth, you will see it blue shifted if the Moon approaches Earth and red shifted if the Moon recedes from Earth.

But the effect is tiny.

[lightarrow]

As the moon is moving towards/away from earth, a light from earth would show a nanosecond blue/red shift. This is due to Doppler effect. Agree?

If you are on the Moon observing a light beam from Earth, you will see it blue shifted if the Moon approaches Earth and red shifted if the Moon recedes from Earth.

But the effect is tiny.

Ah, but it depends on what he intended with "if the Moon approaches Earth"; if he intended "during the actual phase of Moon's approachement to Earth" or if he could mean "in a Moon launched at relativistic speed towards the Earth" (because I haven't understood it) [].
Anyway, the effect is perfectly detectable with modern interferometry (even with no relativistic Moon  []).

[lightarrow]

Is it possible to design a "prism" in such a way that blue light is transmitted out while red light is internally reflected.

Yes, it should be possible, chosing the right frequencies of red and blue, the right material and a suitable range of internal incidence angles.