Lesson Plan

• Define the normal, angle of incidence and angle of refraction in ray diagrams.
• Explain how these angles relate through Snell’s law.
• Apply the terms to solve basic refraction calculations.
• Identify common errors when drawing and measuring the angles.

• Projector or interactive whiteboard
• Prepared diagram of a ray incident on a plane surface
• Protractors and rulers for each student
• Worksheet with drawing and calculation tasks
• Scientific calculators
• Exit‑ticket slips

Begin with a quick question about how light changes direction when it passes from air into water to spark curiosity. Review that students already know about straight‑line propagation and basic reflection. State that by the end of the lesson they will correctly label the normal, angle of incidence and angle of refraction and use these to apply Snell’s law.

1. Do‑now (5 min): short quiz on reflection terminology.
2. Mini‑lecture (10 min): introduce/define normal, i and r with a projected diagram.
3. Guided drawing (15 min): students draw the ray diagram on worksheets and label all angles.
4. Snell’s law demonstration (10 min): work through the air‑to‑water example using calculators.
5. Collaborative problem solving (15 min): groups solve two new refraction scenarios, teacher circulates for checks.
6. Misconception check (5 min): quick poll on common mistakes, clarify correct approach.
7. Exit ticket (5 min): each student writes one correct definition and one error to avoid.

Summarise the key steps for analysing refraction: locate the point of incidence, draw the normal, label i and r, then apply Snell’s law. Collect exit tickets to gauge understanding and assign a worksheet for homework that includes two additional Snell’s law calculations.