The refractive index is central to Snell’s Law because it determines how much light bends when passing from one medium to another. It measures how much the speed of light slows down in a material compared to in a vacuum.
In Snell’s Law, the refractive index shows how optically dense a material is. A higher refractive index means light travels more slowly in that medium. When light moves from a medium with a lower refractive index to one with a higher refractive index, it bends toward the normal. When it goes from a higher to a lower refractive index, it bends away from the normal.
The refractive index difference between two media determines:
- The amount of bending or refraction.
- Whether total internal reflection can occur.
- The critical angle at which total internal reflection begins.
In optics, knowing the refractive indices of materials helps design lenses, prisms, and fiber-optic systems with precise control over light paths. Thus, the refractive index plays a key role in predicting and controlling how light behaves at boundaries between materials.