Why does red travel faster than the other colours?

Answer 1

In a vacuum all colours travel at the same speed, referred to as 'c', however in a transparent medium such as glass, the light waves are slowed down, the ratio of the speed in a vacuum to that in the medium is the refractive index. There is also an effect which depends on the wave frequency, such that the higher the frequency the more it is slowed. Red light is at the low end of the visible spectrum of frequencies, and violet at the high end. If you look carefully at the refraction of natural light through a prism, you will see that the red is turned through a lower angle than the violet. This effect is called dispersion, and it is due to the different frequencies in the natural light. This effect is also seen in rainbows.