When a ray of light crosses the surface of a translucent medium of different density, its speed and direction change (it is [i]refracted[/i]) according to Snell's Law.

NOTES:[br]Constants η_1, η_2 are the Indices of Refraction (IOR) of the two media. [br]The IOR of a substance is determined by observation. For convenience, we take IOR of air = 1.[br][br]In words, for any two given media,[i] the ratio of sines of the two angles is a constant[/i].[br][br]In general, two rays result. A fraction of the incident ray is reflected, and a fraction is transmitted into the new medium.[br][br]________[br]Reflection and Refraction[br]1. Reflect a ray: [url]http://www.geogebratube.org/material/show/id/111895[/url][br]2. One side is reflective: [url]http://www.geogebratube.org/material/show/id/112443[/url][br]3. Lamp: [url]http://www.geogebratube.org/material/show/id/112549[/url][br][b]→4. Refract a ray[/b][br][br]These are my self-study materials. Let me know how I can make them more useful to you.