what is meant by refractive index?

The refractive index (also called the index of refraction) is a measure of how much light slows down and bends when it passes from one medium into another.

Key points:

Definition: It's the ratio of the speed of light in a vacuum to the speed of light in a specific medium:

n = c/v

where:

• n = refractive index
• c = speed of light in vacuum (~300,000 km/s)
• v = speed of light in the medium

What it tells us: A higher refractive index means light travels slower through that material. For example:

• Air: n ≈ 1.0003 (light travels almost as fast as in a vacuum)
• Water: n ≈ 1.33 (light travels about 25% slower)
• Glass: n ≈ 1.5 (light travels about 33% slower)
• Diamond: n ≈ 2.42 (light travels much slower)

Why it matters: When light enters a medium with a different refractive index at an angle, it bends (refracts). This bending is what makes:

• A straw appear bent in a glass of water
• Lenses work in glasses and cameras
• Prisms split white light into colors
• Diamonds sparkle

The greater the difference in refractive index between two materials, the more dramatically light bends at their boundary.