Why light can be trapped inside glass or water, the critical angle, and how optical fibres and endoscopes use it.
What you will learn
- State the two conditions for total internal reflection
- Say what happens below, at and above the critical angle
- Work out angles of incidence in blocks and prisms
- Explain how optical fibres and endoscopes carry light
Which boards ask for this
- Edexcel (Physics 1PH0): Physics only. Explain reflection, refraction and total internal reflection with ray diagrams, including the critical angle.
- AQA (Physics 8463): fibre optic communication is listed as a use of visible light. The critical angle is not a separate statement, but it is the reason fibres work.
- OCR Gateway (Physics A J249): reflection and refraction are in P5, but total internal reflection and the critical angle are not in the specification.
None of the boards asks you to calculate a critical angle from an equation at GCSE, so in this lesson critical angles are always given.
The rest of this lesson and its 23 practice questions are locked.
In this lesson
- Which boards ask for this
- Below, at and above the critical angle
- Angles in blocks and prisms
- Optical fibres and endoscopes
- Try it: Trap the light in the refraction sim
- Try it: An easy one first
23 practice questions, marked as you go; about 25 minutes in all.
Key terms
Away from the normal, Critical angle, Total internal reflection, Finding the critical angle, Optical fibre
In this unit: Lenses, visible light, sound and black bodies
Reflection and the glass block practical, total internal reflection and optical fibres, colour and filters, lenses and magnification, sound and echoes, ultrasound and seismic waves, and black body radiation (Physics only).
- Reflection, and the glass block practical
- Colour and filters
- Lenses and magnification
- Sound waves, hearing and echoes
- Ultrasound and seismic waves
- Black body radiation
- Total internal reflection and optical fibres