In a vacuum, which colour of light travels fastest  red, blue, or green? Explain. Which colour travels fastest in a block of glass?

In vacuum

v(red)=v(blue)=v(green)= c=3 x10^8 m/s
In glass
v(red)>v(green)>v(blue)

In a vacuum, all colors of light travel at the same speed, which is approximately 299,792,458 meters per second (or about 186,282 miles per second). This speed is known as the speed of light and is denoted by the symbol 'c'.

To understand why all colors of light travel at the same speed in a vacuum, we need to look at the properties of light. Light is an electromagnetic wave, which means it consists of both an electric field and a magnetic field oscillating perpendicular to each other. The speed of light in a vacuum is determined by the interaction between these fields and the properties of vacuum itself.

Now, let's consider the second part of your question - the speed of light in a block of glass. When light enters a medium like glass, its speed decreases due to interactions with the atoms or molecules of the material. This decrease in speed is a result of the refractive index of the material.

The refractive index of a medium is a measure of how much light slows down when passing through it compared to its speed in a vacuum. Each color of light interacts differently with the atoms of the material, which leads to a phenomenon called dispersion.

Dispersion causes different colors of light to bend at different angles as they pass through the medium, which results in the separation of the colors. This phenomenon is what allows us to see a rainbow when light passes through raindrops, for example.

In the case of glass, the speed of light is slower than in a vacuum, and the extent to which it slows down depends on the wavelength or color of the light. Generally, red light travels slightly faster in glass compared to blue light. This is why when white light passes through a prism, it is spread out into its constituent colors, with red being bent the least and blue being bent the most.

So, to summarize, in a vacuum, all colors of light travel at the same speed, while in a medium like glass, different colors travel at slightly different speeds due to their interaction with the atoms or molecules of the material.