Reflection & Refraction
What happens when a wave hits a boundary? Bounce it off with the law of reflection, bend it as it changes speed with refraction, and learn the one rule that catches everyone: measure from the normal.
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Reflection & Refraction 🪞
When a wave reaches a **boundary** between two materials, it can **bounce off** (reflect), **bend** as it passes through (refract), or be **absorbed**. Get these two behaviours straight — and one golden rule about measuring angles — and boundary questions fall into place.
Reflection and the normal ↩️
In **reflection** a wave bounces off a surface. To describe it we first draw the **normal**: a line at **90° to the surface** at the point where the wave hits. The ray arriving is the **incident ray**; the ray leaving is the **reflected ray**. All angles are measured from the **normal** — never from the surface itself.
Label the reflection
An interactive activity.
The law of reflection 📐
The **law of reflection** is short and exact: **angle of incidence = angle of reflection.** Both are measured from the normal. So a ray hitting a mirror at 30° to the normal leaves at 30° to the normal on the other side.
Angle of reflection
An interactive activity.
The law of reflection
Pick the TWO statements that are correct about the law of reflection.
- The angle of incidence equals the angle of reflection
- The angles are measured from the normal
- The angles are measured from the mirror surface
- The reflected ray bends towards the normal
Order the experiment
An interactive activity.
Refraction 🔀
**Refraction** is the **bending** of a wave as it crosses a boundary into a new material and **changes speed**. Light slows down going into a denser material (like glass) and speeds up coming out. It only bends if it hits the boundary at an angle — straight on, it carries on without bending.
Which way does it bend?
A ray of light travels from air into glass, slowing down. Which way does it bend?
- Towards the normal
- Away from the normal
- It does not bend at all
- Straight back the way it came
Match each term to its meaning
- Normal
- Incident ray
- Reflected ray
- Refraction
- A line at 90° to the surface, used to measure angles
- The wave arriving at the surface
- The wave bouncing back off the surface
- A wave bending as it changes speed
At a boundary 🚪
When a wave meets a boundary, **three** things can happen, and often several at once: • **Reflection** — it bounces back. • **Transmission** — it passes through (and usually refracts). • **Absorption** — its energy is taken in by the material.\n\nWhich one dominates depends on the wave and the two materials.
The boundary rules
In reflection, the angle of incidence equals the angle of _____, both measured from the _____. In refraction, a wave that slows down bends _____ the normal.