Aim: How can we explain critical angle and total internal reflection?

1. Aim: How can we explain critical angle and total internal reflection? Do Now: A ray is traveling from flint glass to air with an angle of incidence of 37.042°. What is the angle of refraction? n1sinθ1 = n2sinθ2 1.66(sin37.042°) = 1.00(sinθ2) sinθ2 = 90°

2. Critical Angle • When light travels from more dense to less dense, ray bends away from normal • This θr can eventually reach 90o • The incident angle that creates this 90° refraction is called the Critical Angle

3. Critical Angle n n θr = 90° θc n n When θi = θc: θr = 90°

4. Critical angle when going into air n1sinθ1 = n2sinθ2 n1sinθc = (1.00)sin90° n1sinθc = 1

5. What is the critical angle for diamond? What is the critical angle for water?

6. Total Internal Reflection TIR Demo • When θi is greater than θc, the incident ray is totally internally reflected • Follow the Law of Reflection • θi = θr

7. n n θi θr n n

9. A light ray incident on diamond hits at an angle of 38°. • What will the light ray do? • Reflect • b. What will be the angle of reflection? • 38°

10. Remember! • For TIR, two conditions must exist: • The light ray must try to go from a high to a lower index of refraction • The angle of incidence must be larger than the critical angle

11. Applications • Fiber Optics!!!

12. Diamonds!!