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Partial internal reflection
- Under certain circumstances the transparent boundary between one material and one of lower refractive index can act like a perfect mirror to particular incident rays.
- Whenever a wave crosses a boundary between materials there is always some level of reflection.
- Reflections are always partial reflections
- i.e. the energy of the reflected ray is not equal to the energy of the incident ray.
- Even the metal coatings used to make mirrors absorb some incident wave energy.
Total internal reflection
- All rays are reflected (bounce) off the internal walls with no energy loss. This is known as Total Internal Reflection.
- Total internal reflection reflects 100% of the light, subsequent absorption by the glass media and/or boundary losses will reduce to partial internal reflection.
- It only occurs under the following conditions:
- the ray must be travelling from a material of higher Absolute Refractive Index to lower Absolute Refractive Index.
- The angle on incidence at the boundary is greater than the Critical Angle, θc
Critical Angle
In AS/A-Level Physics, the critical angle (θc) is an angle of incidence which produces an angle of refraction of 90o.
And we're all done for today!
