IGCSE Physics Refraction | Waves #3 | Snell’s Law, Critical Angle & Total Internal Reflection

Welcome to Lesson 3 of the IGCSE Physics Waves Course.

In this lesson, we explore one of the most important topics in the Waves chapter: Refraction. We will build a complete understanding of why waves bend when they enter a new medium, how wavelength and speed change during refraction, and how these ideas lead to the concepts of Critical Angle and Total Internal Reflection (TIR).

This lesson also covers wavefront diagrams, optical fibres, apparent depth and Snell’s Law calculations commonly tested in IGCSE examinations.

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In This Lesson

✅ What is refraction?

✅ Why waves bend at a boundary

✅ Refraction of wavefronts

✅ Refraction in deep and shallow water

✅ Refraction from rarer to denser media

✅ Refraction from denser to rarer media

✅ Why no bending occurs along the normal

✅ Changes in speed, wavelength and frequency

✅ Critical Angle

✅ Total Internal Reflection (TIR)

✅ TIR Formula

\sin c = \frac{1}{n}

✅ Snell’s Law

\frac{\sin i}{\sin r}=\frac{n_2}{n_1}=\frac{v_1}{v_2}

✅ Optical Fibres

✅ Endoscopy

✅ Apparent Depth

✅ Common IGCSE Exam Questions

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Course Resources

Course Resources

📋 Waves Chapter Checklist
[https://docs.google.com/spreadsheets/d/1ZSOy558gRdPQzFKZy7Qj3I4lYk8o6kbBp6BZAWEIen4/edit?usp=sharing]
📚 IGCSE Physics Books & Reference Material
[P2 Topical Past Paper Book-https://drive.google.com/file/d/1XF3Qf3qUtimnffKHRO9jQPsdyoBjUESV/view?usp=share_link
P4 Topical Past Paper Book-https://drive.google.com/file/d/1ETFxGffdV2dhku4pUbeNTPf1z71hDwoa/view?usp=share_link
P6 Topical Past Paper Book-https://drive.google.com/file/d/14ULh7qMwpoA4sBNw4tbNgfPOkYlQBGYl/view?usp=share_link ]

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Notes for This Video

📄 Lesson-specific notes, diagrams and worksheets:

[https://drive.google.com/file/d/1famqKLcTQsMt7OCt2HoAfNBwCfDSYZcx/view?usp=sharing]

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By The End Of This Lesson You Should Be Able To

• Explain why refraction occurs

• Predict the direction of bending during refraction

• Draw accurate refraction wavefront diagrams

• State how speed, wavelength and frequency change during refraction

• Calculate critical angle

• Solve Snell’s Law problems

• Explain Total Internal Reflection

• Draw optical fibre ray diagrams

• Explain apparent depth

• Apply these concepts to IGCSE examination questions

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This lesson is designed around a checkpoint-based approach focused on deep conceptual understanding, accurate diagram interpretation and examination success.

🌐 More Physics, Additional Mathematics and IB Mathematics resources:

www.ezeemath.com

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