2. PERIPHERAL VISION 1.Take off your glasses if you wear them. 2.Stare straight ahead at the blackboard. 3.Close your right eye. 4.Hold the index finger of your right hand in a horizontal position, pointing forward, at arm’s length away from your side. 5.While staring straight, slowly rotate your right arm forward until you can just see your index finger with the peripheral vision of your left eye. 6.Rotate your left eye, not your head, to look at your index finger.

3. WHAT HAPPENED?  Light that just passes by your nose strikes the eye’s lens and refracts (BENDS) in to your eye.

4. LEFT EYE ROTATION  When you rotate your left eye, your finger should disappear behind your nose.  WHY?  There is no straight line path between your finger and retina (light sensitive part at the back of your eye).  What do you think would happen if you had on glasses?

5. NO GLASSES VS. GLASSES

6. REFRACTION  What light travels through is called the MEDIUM  Refraction is the bending of light when it passes in to a different medium or a medium with changing density.  All transparent materials (e.g glass, plastic, diamond, etc.) refract light. These materials are said to be OPTICALLY DENSE  In our example, the light is travelling from an Optically LESS Dense material (like air) to an Optically MORE Dense material (like glass and water)

7. SPEED OF LIGHT  The speed of light is 3.0 x 10 8 m/s in a vacuum (in air it is slightly less than this)  In water, however, it is measured at 2.26 x 10 8 m/s  So based on this, when light travels from different media, refraction occurs because of the changing of speed!  It is either slowing down or speeding up.

8. REFRACTION NOMENCLATURE

9. REFRACTION OF LIGHT ACTIVITY  Now we will play with refraction to see if we can find any patterns!

10. INDEX OF REFRACTION  Defined as the ratio of the speed of light in a vacuum to the speed of light in that medium.  Where c = speed of light in a vacuum (3.0 x 10 8 m/s) n = index of refraction (no units) v = speed of light in a medium (m/s)

11. CAN ALSO USE…  The angle of incidence and angle of refraction to calculate the index of refraction…  = Angle of incidence  = Angle of Refraction  NOTE: We will use Theta instead of moving forward

12. SNELL’S LAW  Willebord Snellius (1580 – 1626) stated that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the opposite ratio of the indices of refraction.

13. HOMEWORK  Read sections 12.1 – 12.4  Attempt questions at end of sections