IGCSE Physics: Critical Angle & Total Internal Reflection | Edexcel Modular | Unit 5 | L9

IGCSE Physics: Critical Angle & Total Internal Reflection | Edexcel Modular | Unit 5 | L9

This lesson covers spec points 5.20, 5.21 and 5.22 — defining and calculating critical angle, the conditions for TIR, and applications in optical fibres and prisms.

PowerPoint includes:
• Retrieval starter reviewing Snell’s Law and refraction
• Direct Instruction (I Do) — critical angle defined; TIR conditions stated; sin c = 1/n introduced with worked example for glass (n = 1.5)
• Guided Practice (We Do) — three critical angle calculations (water, diamond, and working backwards from c)
• Independent Practice (You Do) — predicting ray paths at i = 30°, 42° and 55°; endoscope discussion; optical fibre and prism applications
• TIR misconception check: can TIR occur going from air into water? (true/false with reasoning reveal)
• Terminology matching activity
• Review and Reflect exit ticket on dual TIR conditions

Activity Sheet includes:
• Formulae box showing sin c = 1/n
• 11 exam-style questions plus stretch covering critical angle calculation, TIR conditions, optical fibres, prisms, endoscopes
• Q8 includes a blank drawing space for the prism periscope ray diagram
• Prism periscope answer diagram provided separately for teacher use
• Stretch question involves core/cladding refractive index scenario
• Full mark scheme for teacher use