OFFTOPIC: physics question

Peter Fairbrother peter at
Mon May 13 16:43:16 PDT 2019

On 13/05/2019 19:59, \0xDynamite wrote:
>>> If light travels at a. different speed for different colors in order
>>> to account for the rainbow of a prism, how fast is the. speed of light
>>> then?  Is there real physics to optics?  How can light know what
>>> direction to bend after it leaves the lens?
>> The speed of light in glass is slightly less than the speed of light in
>> air. This causes light to be refracted (roughly speaking, change the
>> direction of its path) when it enters glass at an angle.
>> The mathematics of this is called Snell's law, sin(a)/sin(b) = v(a)/v(b)
>> where sin(a) is the angle of incidence, sin(b is the exit angle, v(a) is
>> the velocity of light in air and v(b) is the velocity of light in glass.
> Thanks for your response.  The problem with Snell's Law, AFAIK, is
> that there are actually two angles of incidence to account for since
> there are two dimensions to its surface.

No, there is only one angle between a line and a plane.

>> However, light of different frequencies travels at different speeds in
>> glass. Thus blue light bends more than red light, and if the light
>> travels through a triangular prism the familiar spectrum is formed.
> Yes, this is the part where science "fills in the gaps" it seems
> without just cause.  Is light a physical constant > dependent on
> material properties 

The speed of light in a vacuum is constant. The speed of light in glass 
depends on its wavelength.

This is known as dispersion. The amount (and direction) of the 
dispersion depends on the type of glass.

> or is the lens effecting different frequencies differently 


 > or does light change speed for the viewer.


> I think the only way to account for the axiis of a lens (even though
> it may be symmetrical), is through the relationship to the viewer.
> Ie. it is both subjective and objective phenomenon.

now you have lost me

Peter F
> Mark

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