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Science presenter Jon Chase explains total internal reflection. He demonstrates how total internal reflection can make a coin disappear inside a glass of water and bend a laser beam. The second demonstration is used as a model for fibre optics.
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First broadcast:
11 May 2012

Classroom Ideas

The class could repeat the demonstration with the glass and the coin. Ask them to draw light ray diagrams to show what happens when they move their head higher or lower. There are a variety of ray diagrams possible, depending on the position of the viewer and the amount of water in the glass.
Students could also investigate total internal reflection using ray boxes and blocks of Perspex and glass, measuring the critical angle in each case. Total internal reflection could also be demonstrated by the teacher using a laser beam shining through these blocks, or even through a rectangular block of gelatine.

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