Partial Refraction
When looking at a body of water (like a lake or a swimming pool) on a sunny day, sometimes you are blinded by the glare of the Sun off the water. Light passes through the water, as well as being reflected.
When light strikes any interface between two media, some of it reflects back, while some of it refracts through the second medium.
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| When light travels from air to water, some light reflects from the surface and some light travels into the water and refracts. |
This is the partial reflection and refraction of light.
Conditions for Total Internal Reflection
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| In diagrams A and B, the angle of refraction is increasing more rapidly than the angle of incidence. In diagram C, the angle of refraction has reached 90°, making the angle of incidence the critical angle. At all angles beyond the critical angle, as in diagram D, all light is internally reflected. |
Notice
that the refracted light bends away from the normal.
For all angles of refraction up to and including 90°, the light is reflected and refracted at the same time.
The amount of reflected light gradually increases and the amount of refracted light gradually decreases as the angle of incidence increases.
The angle of refraction increases more rapidly than the angle of incidence.
The angle of incidence for which the angle of refraction equals 90° is called the critical angle.
When angle of incidence is greater than the critical angle, all the incident light is completely reflected.
The boundary now behaves as if it were a perfect mirror and there is total internal reflection.
This phenomenon is the reason why diamonds sparkle.
Watch this video (watch until 6:07) for more info.
Fibre Optics
Read p. 339.
Question of the Day #11: List two reasons why optical fibres are preferred over copper wires for many types of communication.
