Reflection vs Refraction — What's the Difference?
Reflection
Reflection is the bouncing of light off a surface back into the same medium. The angle of incidence equals the angle of reflection, both measured from the normal.
Unit: degrees (angle)
Example: Seeing your face in a bathroom mirror: light from your face strikes the mirror and reflects to your eyes with angle in equal to angle out.
Refraction
Refraction is the bending of light as it passes from one medium into another with a different optical density, because its speed changes.
Unit: degrees (angle); n is unitless
Example: A straw in a glass of water looks bent at the surface: light slows down entering water, so rays bend and the straw appears displaced.
Key differences
| Aspect | Reflection | Refraction |
|---|---|---|
| What happens | Light stays in the same medium | Light enters a different medium |
| The law | θi = θr — angle in equals angle out | n₁sinθ₁ = n₂sinθ₂ — speed change bends the ray |
| Speed change? | No — speed in the medium is unchanged | Yes — slower in glass than in air, which causes the bending |
| Everyday result | A mirror image | A straw looking bent in a glass of water |
| Special case | Total internal reflection (fiber optics) | Dispersion — prism splitting white light into colors |
Students mix up which law uses which angle: both reflection and refraction measure angles from the normal (the perpendicular), not from the surface. A ray hitting straight on (0° from the normal) reflects straight back and refracts with no bending at all — the bending only appears at an angle.