Students use the wave model to explain reflection and refraction: wave fronts bounce at equal angles, and slow down and bend towards the normal in a denser material (AC9S9U04, node 4; builds on AC9S5U03).
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Engage and Explore 8 min · Explain 10 min · Evaluate 3 min · Typical adds 4 min, Wider about 2 min
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It follows What is the electromagnetic spectrum? and comes before Wave or particle?
Students met reflection and refraction as rules for rays in Year 5. Here the wave model gives the reason. The blue lines are wave fronts (crests); the orange arrows are rays, at right angles to the fronts.
Board notes: the wave fronts' spacing in the second material is the incident spacing divided by the refractive index (1.33 water, 1.5 glass, 2.4 diamond); the ray's angle follows Snell's law. The light is a single colour, so dispersion isn't shown. Partial reflection at the glass is drawn as a dotted line. The index and Snell's law are not named for students.
Connecting a change of speed to a change of direction. When a student says 'the glass bends it', ask what happens to one end of the wave front when it slows down first.
| What you will see | A question to ask | The fix |
|---|---|---|
| A student measures the angle from the surface. | Which line are both angles measured from on the board? | The normal, the dashed line at right angles to the surface. |
| A student says light speeds up in glass. | Are the fronts closer together or further apart in the glass? | Closer: the waves are slower there. |
| A student says a ray along the normal bends. | Which end of the front enters the glass first? | Neither: the whole front enters together, so it slows without turning. |
One possible solution for each task. Other correct programs are fine.
Open task: any program that does what the step asks.
Open task: any program that does what the step asks.
Open task: any program that does what the step asks.
Stretch: Water bends light less than glass. Is light faster or slower in water than in glass? (Faster: water slows it down less.)
Support: Give a marching-band picture: a line of people walks from pavement onto sand at an angle and slow down one by one. Students draw the line turning.
For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.
You are a patient science coach for a Year 9 student in Australia. Help me understand ONE idea only, from the lesson "How does light bend?". The idea: The wave model of light and electromagnetic radiation: I can describe light and electromagnetic radiation as waves and explain how the wave model accounts for phenomena including reflection, refraction and the electromagnetic spectrum. What understanding looks like: - Describes light as a transverse wave and the EM spectrum as a family of waves differing in frequency and wavelength - Uses the wave model to explain reflection and refraction - Explains how wave frequency relates to energy across the electromagnetic spectrum Mistakes students often make here: - A student measures the angle from the surface. - A student says light speeds up in glass. - A student says a ray along the normal bends. How to coach me (rules from the Waypoints Kit coach): - Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question. - Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit). - If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go. - If I seem to be missing the idea that comes before this one (The particle model of electricity — static charge and current), check it quickly, then come back. - Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back. - After you help, ask me one reflective question, such as how I know my answer is right or what I would check. - Praise my effort and method, not my ability. - You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so. - Use simple words. - Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "How does light bend?".
A ray of light goes from air into water and bends towards the normal. What does that tell you about the speed of light in water?
It is slower in water than in air. The change of speed turns the wave fronts and so the ray.
Next: Wave or particle? weighs up the wave and particle models.
In class: a laser pointer through a tank of water, a clear block or a semicircle; a coin in a cup that appears when water is poured in; a mirror and a ruler for the law of reflection.