Lesson Plan

• Recall the relationship between refractive index and the critical angle.
• Derive the equation n = 1 / sin c from Snell’s law.
• Apply the equation to calculate either refractive index or critical angle for common media.
• Explain how refractive index influences total internal reflection and the sparkle of materials such as diamond.
• Solve multi‑step problems involving refraction and critical angles.

• Projector or interactive whiteboard
• Printed worksheet with practice questions
• Glass, water and acrylic blocks for a ray‑tracing demo
• Scientific calculators (or calculator app)
• Handout of typical refractive indices
• Whiteboard and markers

Begin with a quick demonstration of a laser beam striking a glass block to show a bright reflected ray. Ask students what determines whether the ray is reflected or refracted, linking to prior knowledge of Snell’s law. Explain that by the end of the lesson they will be able to predict the critical angle and use the equation n = 1 / sin c confidently.

1. Do‑now (5') – Students calculate the critical angle for glass‑air (n = 1.52) and record the answer.
2. Mini‑lecture & derivation (10') – Teacher derives n = 1 / sin c from Snell’s law, using the projected diagram.
3. Guided example (12') – Work through the provided worked example together, highlighting each algebraic step.
4. Hands‑on activity (10') – Small groups use glass blocks and a laser pointer to observe total internal reflection; they measure the angle at which it occurs.
5. Independent practice (10') – Students complete the three practice questions on the worksheet.
6. Check for understanding (8') – Quick Kahoot quiz on definitions, the equation, and common mistakes.
7. Summary & exit ticket (5') – Each student writes one calculation they can now perform using n = 1 / sin c.

Review how the critical angle links refractive index to total internal reflection and revisit the key equation. Collect exit tickets to gauge mastery and assign homework: complete a set of five additional problems requiring calculation of either n or c for various media.