TOTAL INTERNAL REFLECTION

1. TOTAL INTERNAL REFLECTION Textbook Reference: p. 338 - 338

2. 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.

4. 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. • When light moves from one substance to another, some light reflects, some light refracts

5. Some light refracts into the glass, some light reflects from the glass. How much depends on the angle of the incident ray.

6. Why can you not see beneath the surface of the water? Because the angle of incidence is great, most of the sunlight reflects from the water’s surface. Very little goes into the water.

7. 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.

8. When going from a faster to a slower medium light bends (refracts) toward the normal.

9. We have also learned that when light goes from a slow medium to a fast medium the light (refracts) bends away from the normal.

10. From fast to slow (e.g. AIR to WATER), some light will always enter the second substance. • Even when the angle of incidence is large (just along the boundary!)

11. When light travels from a slow medium to a faster medium (E.g. WATER TO AIR) something very interesting happens. • Look at the next series of pictures.

15. Where does the light go?

16. It is all reflected. No light escapes!

17. Note: This only happens when light is moving from a “slower” substance to a “faster “ substance.

18. The incident angle at which a 90 degree refracted ray is produced is called the CRITICAL ANGLE Critical Angle

21. DEMO TIME!

22. Applications of Total Internal Reflection

23. Glass Prisms –When light enters the long side of the prism at any angle, it is reflected back out of the prism at 180 degrees (same direction the light entered the prism!) One use of prisms is in binoculars

24. Retroreflectors • small plastic prisms that also reflect light directly back

28. The cutting of gemstones (e.g. diamonds)

29. The shape of the diamond will determine the sparkle of the diamond!

30. FIBRE OPTICS • Made from a thin glass fibre and covered with a another type of glass (like a sleeve) • Light is totally internally reflected along the entire fibre • Groups of fibres are bundled and can be up to several kilometres long.

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

33. Uses of Fibre Optics

34. Telecommunications to carry information (e.g. Phone / cableTV / internet)- carries more signals than copper wires- smaller and lighter- not affected by electrical storms The small optical fibres on the left can carry as much information as the larger copper cable on the right.

35. Medicine- endoscope (much less invasive surgery), allows doctors to see inside (light and camera)

37. Toys and art too 