Reflection – Ray Diagrams Simulation
This interactive simulation shows how light rays behave when they strike a reflecting surface. Pupils can switch between five surface types — flat mirror, concave mirror, convex mirror, water surface, and rough surface — and control the angle of incidence in real time using a slider or by clicking directly on the canvas.
The normal is shown at the point of incidence, with labelled angle arcs carrying double tick marks on both θᵢ and θᵣ to illustrate visually that the angles are equal. On the water surface, a reflected ray and a refracted ray (gold) are both drawn simultaneously, with the refraction angle calculated live from Snell’s law (n = 1.33). The metrics bar displays the angle of incidence, angle of reflection, and — in water mode — the refraction angle θₜ.
Class Activity — The Law of Reflection in Action
Year 9/10 · ~50 min · Pairs
Objective: Observe and verify the law of reflection across different surfaces; extend to refraction at a water boundary.
Hook (5 min) Open on Flat mirror. Ask: “I’m going to change this slider — predict what happens to the reflected ray.” Take responses, then move it. Most pupils predict correctly. Ask: “What would happen at a bumpy surface?” Switch to Rough — let the surprise land.
Structured Exploration (15 min) Pupils work through these tasks, recording observations:
- Set any angle on Flat. Read θᵢ and θᵣ. What do you notice?
- Try five different angles. Does the pattern hold every time?
- Switch to Concave with 3 rays. Where do the reflected rays meet?
- Switch to Convex. Do the rays converge or diverge?
Key Question (whole class, 5 min) “The tick marks on both arcs look identical. What are they telling you?” Draw out the law: θᵢ = θᵣ, measured from the normal.
Water and Refraction (10 min) Switch to Water. Ask pupils to record θᵢ and θₜ at three different angles and complete the table:
| θᵢ | θₜ | Is θₜ bigger or smaller than θᵢ? |
|---|---|---|
| 20° | ||
| 40° | ||
| 60° |
Ask: “The gold ray bends toward the normal entering the water. Why?” Introduce n = 1.33 and Snell’s law as the explanation.
Exit Ticket (5 min)
- A ray hits a flat mirror at 35° to the normal. What is the angle of reflection?
- Why is the refracted ray in water closer to the normal than the incident ray?
- In one sentence: why does a rough surface not produce a clear reflection?