Reflection and refraction: measure from the normal
In reflection, the angle of reflection equals the angle of incidence. Both are measured from the normal to the surface. Refraction into a higher-index medium bends an obliquely incident ray toward the normal.
| Observation | What it means |
|---|---|
| Reflection: incidence 30° to normal | reflection 30° to normal |
| Air → glass at oblique incidence | bends toward the normal |
One worked example
- Ray makes 40° with the mirrorThat is not the incidence angle.
- Incidence = 90 − 40 = 50°Switch from the surface to the normal.
- Reflection angle = 50°Apply equal angles.
Watch out: At normal incidence refraction does not change direction. Reflection and refraction can occur together; total internal reflection has specific conditions.
Goal, prerequisites and card origin
What you will learn: Distinguish reflection from refraction.
What you need first: Angles and perpendicular lines.
An original PEAZIT working card. Independent expert review and effectiveness testing have not yet taken place. · v1
Reference for the underlying principle ↗Show connections
In reflection, the angle of reflection equals the angle of incidence. Both are measured from the normal to the surface. Refraction into a higher-index medium bends an obliquely incident ray toward the normal.