Light is travelling in quartz, which has an index of refraction of 1.458. How fast does light travel in quartz?

The definition of the index of refraction is ##n = c / "v"## where ##c## is the speed of light in a vacuum (##3 xx 10^ 8## ##m##/##s##) and ##"v"## is the speed of light in the material.

See if you can use this to figure the speed of light in quartz, since you know the index of refraction.