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Partial Reflection & Refraction

Partial Reflection & Refraction. What do a fish pond, an office building, and a pair of sunglasses have in common?. - When light strikes these objects some of it is reflected , but a great deal is refracted at the same time. Partial Reflection and Refraction.

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Partial Reflection & Refraction

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  1. Partial Reflection & Refraction What do a fish pond, an office building, and a pair of sunglasses have in common? - When light strikes these objects some of it is reflected, but a great deal is refracted at the same time.

  2. Partial Reflection and Refraction • Sometimes you can see through a window to the other side as well as a reflection of yourself or another object on ‘your’ side.

  3. Partial Reflection and Refraction • When two media have different indices of refraction (n), some light reflects, some light refracts. • How much refracts and how much reflects will depends on 1) the angle of incidence 2) indices of refraction (n) of the two substances.

  4. Why can you not see beneath the surface of the water? Because the angle of incidence is great, most of the sunlight is being reflected from the water’s surface.

  5. Why can you see beneath the surface closer to you? Because the angle of incidence is small (the sun is overhead), most of its rays are refracted into the water and little is reflected.

  6. TOTAL INTERNAL REFLECTION Textbook Reference: p. 461 - 466

  7. Total Internal Reflection • When going from a faster to a slower medium (n2>n1), light bends toward the normal.

  8. Total Internal Reflection • We have also learned that when light goes from a slow medium to a fast medium (n2<n1) that the light bends away from the normal.

  9. Total Internal Reflection • When light travels from a fast medium to a slow medium, then increasing the angle of incidence increases the angle of refraction.....but some light always enters the slow medium even if the angle of incidence is close to 90 degrees.

  10. http://www.mytextbook.ca/product/9780070318571/itr/ppt/Ch11_SLIDE_10.p450_Reflect_Refract_Simulation_REV.swf.htmlhttp://www.mytextbook.ca/product/9780070318571/itr/ppt/Ch11_SLIDE_10.p450_Reflect_Refract_Simulation_REV.swf.html

  11. However, when light travels from a slow medium (like water) to a faster medium (like air), something very interesting happens. • Look at the next series of pictures.

  12. Where does the light go?

  13. It is all reflected. No light escapes!

  14. http://www.mytextbook.ca/product/9780070318571/itr/ppt/Ch11_SLIDE_10.p450_Reflect_Refract_Simulation_REV.swf.htmlhttp://www.mytextbook.ca/product/9780070318571/itr/ppt/Ch11_SLIDE_10.p450_Reflect_Refract_Simulation_REV.swf.html

  15. The incident angle at which a refracted ray is produced along the boundary is called the CRITICAL ANGLE.

  16. DEMO TIME!

  17. Applications of Total Internal Reflection

  18. Applications of Total Internal Reflection • Glass Prisms – shaped like an isosceles right triangle. When light enters the long side of the prism at any angle, it is reflected back by the two short sides and out of the prism in the opposite direction it went in. One use of prisms is in binoculars

  19. Applications of Total Internal Reflection • Retroreflectors • small plastic prisms that also reflect light directly back (ie. by 180 degrees) regardless of the direction of incident light.

  20. Applications of Total Internal Reflection • The cutting of gemstones (e.g. diamonds)

  21. The “sparkle” of diamonds is due to internal reflection.

  22. Applications of Total Internal Reflection • FIBRE OPTICS • Made from a glass core and covered with a sleeve (cladding) – often another type of glass • ncladding < nglass core • Light enters the fibre (core) at an angle less than the critical angle and the light is totally internally reflected along the entire fibre • Groups of fibres are bundled and can be up to several kilometres long.

  23. If each incident angle is greater than the critical angle, the light will not escape

  24. Fibre Optics (continued)

  25. Fibre Optics (continued) • Used in Telecommunications to carry information (e.g. Phone / cableTV / internet)- can carry many more signals than copper wires- smaller and lighter- not affected by electrical storms • Used in Medicine- endoscope(much less invasive surgery), allows doctors to see inside (light and camera) • And even do complex surgery inside the body using a laparoscope.

  26. The small optical fibres on the left can carry as much information as the larger copper cable on the right.

  27. And just for fun!! • Toys and fountains etc.

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