What is the index of refraction, and how does it relate to the speed of light in different substances?
The index of refraction is the relationship between the speed of light in a vacuum and the speed of light in a substance. Different materials have characteristic electrical properties, and when light moves from one medium to another, it must adjust to the local environment, leading to changes in speed and direction. This index is crucial in understanding how light behaves in transparent materials like glass, water, and diamonds.