2. Last lesson Light travels faster than sound Using ray boxes The law of reflection

3. Reflection Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror Angle of incidence = Angle of reflection

4. Mirror Island

5. Today’s lesson Refraction of light

6. The mug trick!

7. An Investigation What does water do to the path of light? Can we explain the “Mug Trick’? “Mirror Island II” due in Monday 25 th !

8. Gather round!

9. Mug Investigation You are going to pass light through the blocks without water and with water Draw around the block and pass light through (at a point and angle of your choice) Trace the path of the beam. Keeping everything in the same position, pour water in and record where the beam goes. Repeat for 2 different positions/angles Join the lines to show what happens INSIDE the block. Title

10. Refraction of light Glass block Beam of light Glass block Beam of light

11. 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 Can you copy this please?

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

13. Water waves Water waves travel slower in shallow water

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

15. 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

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

17. 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)

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

19. Let’s try some questions! Page 147 Questions 1, 2 and 3.

20. Measuring refractive index i r Ray, NOT wavefronts refractive index (η) = sin(i) sin(r)