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### 13 lenses

1. 1. LENSES REFRACTION AND TIR
2. 2. Refraction (Ray Property) • REFRACTION is the change of direction of light when it passes from one medium to another or of different optical density. • Optical density has something to do with the transparency of a substance to light. Light travels slowly in an optically dense medium.
3. 3. Index of Refraction (n) • - property of a substance which refers to ratio of the speed of light in a vacuum ( c ) to the speed of light in the substance • OPERATIONAL DEFINITION: n = c / v where: c = 3 x 108 m/s and v is the velocity of light in the medium
4. 4. Example Table Index of Refraction of Some Materials ( for Yellow light ): Materials n Materials n air 1.0003 glass (crown) 1.5230 ice (at 0°C) 1.3090 sapphire 1.7700 water 1.3300 zirconium 2.2000 fused quartz 1.4600 diamond 2.4190
5. 5. The Law of Refraction 1. The incident ray, refracted ray and the normal line lie in one plane. 2. When a ray of light passes obliquely from an optically dense medium, it is refracted away from the normal line. 3. When a ray of light passes obliquely from an optically less dense medium, it is refracted toward the normal line. 4. At perpendicular incidence, no bending of light ray occurs.
6. 6. Snell’s Law Visualization
7. 7. Spherical Lens - any piece of glass or transparent material having at least one spherical surface Types: 1. Convex Lenses – lenses that are thicker at the middle than at the edges; also called converging lenses 2. Concave Lenses – lenses that are thicker at the edges than at the middle; also called diverging lenses
8. 8. Specific Lens Types
9. 9. Physics and Contact Lenses Myopia (Nearsightedness) occurs when light rays are focused in front of the retina. Close objects can be seen clearly but objects at a distance are out of focus. Lenses that are thinner in the center than on the edges (concave) increase the focal length.
10. 10. Physics and Contact Lenses Hyperopia (Farsightedness) is a condition in which light rays are focused behind the retina. Distant objects can be seen clearly but close objects are out of focus. Lenses that are thicker in the center than on the edges (convex) decrease the focal length.
11. 11. • fin
12. 12. White Light Refraction
13. 13. Total Internal Reflection • When light passes from a dense substance into a less dense substance, there is an angle, called the critical angle, beyond which 100 percent of the light is reflected from the surface between substances. • Total internal reflection occurs when light strikes the boundary between substances at an angle greater than the critical angle.
14. 14. The Law of Refraction Snell’s Law (Willebrord Snell) : n1sinθi = n2sinθR where: n1 - index of refraction of the 1st medium n2 - index of refraction of the 2nd medium θi - is the angle of incidence θr - is the angle of refraction