Physics frequency and speed

The reason is because light is electromagnetic wave in nature. The speed of propagation of electromagnetic wave in a medium depends on the dielectric constant of that medium. But dielectric constant is frequency dependent, hence the frequency of electromagentic wave (including light) affects the speed of the wave in a medium.

Different coloured lights have different frequencies. This leads to the result that they travel in different speeds in a medium, and hence causes the dispersion effect.

It's generally correct that:

Speed v depends on medium.

Frequency f depends on source.

Wavelength 入= v / f

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And Dispersion is just a special case.
For Dispersion to occur,
the only way to explain that
is different color of light travel with slightly different speed in the prism.

2012-12-05 10:18:26 補充：
The refractive index of materials varies with the wavelength (and frequency) of light. This is called dispersion and causes prisms to divide white light into its constituent spectral colors, and explains how rainbows are formed.

2012-12-05 10:23:11 補充：
it's correct that

Speed of wave depends on Medium;

Freq of wave depends on Source.

2012-12-05 10:23:21 補充：
But one thing more for Refraction of light

is that the refractive index of materials depends on wavelength of light,

for different color of light, their speeds in the materials (prism) are slightly different

and that causes Dispersion of light.