Eduqas A-Level Physics A420QS
Basic Physics
Kinematics
Dynamics
Energy Concepts
Circular Motion
Vibrations
Kinetic Theory
Thermal Physics
Conduction of Electricity
Resistance
D.C. Circuits
Capacitance
Solids Under Stress
Electrostatic and Gravitational Fields of Force
Using Radiation to Investigate Stars
Orbits and the Wider Universe
The Nature of Waves
Wave Properties
Refraction of Light
Photons
Lasers
Nuclear Decay
Particles and Nuclear Structure
Nuclear Energy
Magnetic Fields
Electromagnetic Induction
Option A: Alternating CurrentsOption A
Option B: Medical PhysicsOption B
Option C: The Physics of SportsOption C
Option D: Energy and the EnvironmentOption D
Mathematical Requirements (Appendix C)
Refraction of Light
Total internal reflection and the critical angle
- 3 things to know
- Component 3
Overview
Two conditions required for total internal reflection and critical angle.
What you need to know
Answer each one before you reveal it.
Define the critical angle.
Give the critical angle equation for a boundary with air.
Questions from this subtopic
Each one with the model answer underneath.
- 1
State the two conditions required for total internal reflection.
Model answer
The light must be travelling from a medium of higher refractive index towards one of lower refractive index, and the angle of incidence must exceed the critical angle.
- 2
Define the critical angle.
Model answer
The critical angle is the angle of incidence in the denser medium at which the angle of refraction is ninety degrees.
- 3
Derive the equation for the critical angle at a boundary between two media.
Model answer
Putting the angle of refraction equal to ninety degrees in n₁ sin θ₁ = n₂ sin θ₂ gives n₁ sin C = n₂, since sin90° is one.
- 4
Give the critical angle equation for a boundary with air.
Model answer
sin C = 1/n, where n is the refractive index of the denser medium.
- 5
Calculate the critical angle for glass of refractive index 1.50 in air.
Model answer
sin C = 1 ÷ 1.50 = 0.667, so C is 41.8°.
- 6
Check that critical angle by substituting it back into Snell's law.
Model answer
1.50 × sin41.8° = 1.50 × 0.667 = 1.00, which is 1.00 × sin90°, as the definition requires.
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