1. Last lesson Refraction of light

2. Refraction When a wave changes speed (normally when entering another medium) it may refract (change direction)

3. Water waves Water waves travel slower in shallow water

4. Light waves Light slows down as it goes from air to glass/water

5. Refraction of light Glass block Beam of light Glass block Beam of light

6. Refraction Glass block Beam of light Light going from air to glass bends towards the normal Light going from glass to air bends away the normal

7. Snell’s law There is a relationship between the speed of the wave in the two media and the angles of incidence and refraction i r Ray, NOT wavefronts

8. Snell’s law i r Ray, NOT wavefronts speed in substance 1 = sin(i) speed in substance 2 sin(r)

9. Snell’s law i r Ray, NOT wavefronts In the case of light only, this quantity is called the refractive index (η) η = sin(i) sin(r)

10. Refraction – a few notes The wavelength changes, the speed changes, but the frequency stays the same Ripple Tank Simulation

11. Today’s lesson Critical angle Total internal reflection

12. Critical Angle?

16. Critical Angle Critical angle (when angle of refraction is 90º)

17. Critical Angle Critical angle (when angle of refraction is 90º) Copy! 90º

18. Total Internal Reflection Critical angle sin c = 1/η sin(critical angle) = 1/(refractive index)

19. Read pages 148 to 151

20. Examples of Total Internal Reflection

26. Questions! Page 149 Questions 1,2 and 3.