Prism Refraction/Reflection

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Postby island » Sun May 01, 2005 8:41 am

When you open this link below you might see a text dowload box first. You may cancel this out. You now will see an equilateral prism with a light beam entering it from the left.

To create a right angle prism of the type used in the cat section of the Fresnel lenses click on the top point of the prism and drag upwards and to the left until the top point is directly over the left point of the base.

To observe the change from reflection to refraction when the critical angle is reached, click on the red tip of the light source and slowly move it upwards to change the angle of the light beam entering the prism.

The "I=" numbers show relative light intensity of the light beams, the primary and the secondaries, and these will change when you change the angle of the beam.

Have fun!

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Postby mikev » Sun May 01, 2005 3:14 pm

Boy, that is really neat! Looks like the kind of thing that could be adapted for interactive LH museum/visitor center displays....
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Postby Terry_Pepper » Sun May 01, 2005 4:52 pm

I can see it now - basically, one could use a prism and a laser pointer.
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Postby island » Sun May 01, 2005 5:33 pm

A laser pointer should work well for optics demonstrations. It would be great for a visitor display.

Has anyone ever used a laser pointer from inside a displayed Fresnel lens? Or from outside shining in. I wonder what that would show. It would be interesting to try this.

What we need is for someone to design an interactive Fresnel lens display, one with a light source that can be changed (expanded or concentrated) and can be moved relative to the focal point of the lens.
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Postby Optics » Mon May 02, 2005 6:42 am


That is a great demo! You can really manipulate the sides and light to see what happens. I bet Fresnel would have liked to use this demo. You can also observe the differences in types of glass if you change the number in the little white box below the prism. It starts out with 1.5 for prism which is good for crown glass. Try changing it to 1.6 for prism which is good for flint glass. Then click anywhere on the drawing to see the change. Unfortunately it only works with the original prism setup, but you can still see the result.
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