Total Internal Reflection (Edexcel A Level Physics)

Revision Note

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Lindsay Gilmour



Total Internal Reflection

  • Total internal reflection (TIR) occurs when:

The angle of incidence is greater than the critical angle and the incident refractive index n1 is greater than the refractive index of the material at the boundary n2

  • Therefore, the two conditions for total internal reflection are:
    • The angle of incidence, θ1 > the critical angle, C
    • Refractive index n1 > refractive index n2 (air)

Total internal reflection, IGCSE & GCSE Physics revision notes

Diagram showing refraction, the critical angle and total internal reflection

  • Two conditions are necessary for total internal reflection to occur:
    • The light must be going from a more dense medium into a less dense one
    • The angle of incidence must be greater than the critical angle

Total Internal Reflection, downloadable AS & A Level Physics revision notes

Exam Tip

If asked to name the phenomena make sure you give the whole name - Total Internal Reflection. Remember: Total Internal Reflection occurs when going from a more dense to a less dense material and ALL of the light is reflected. If asked to explain what is meant by the critical angle, you can draw the diagram above (showing the three semi-circular blocks).

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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.