2. Lesson Objectives State how light bends when it travels from a medium of lower index of refraction (less dense, faster) to a medium of higher index of refraction (denser, slower). State how light bends when it travels from a medium of higher index of refraction (denser, slower) to a medium of lower index of refraction (less dense, faster) State the condition under which light travels from one medium to another without bending. Explain the behavior of light using the analogy of a rolling barrel.

3. Revision What is refraction? What is index of refraction ? Lower index of refraction  faster speed (less dense medium) Higher index of refraction  slower speed (denser medium)

4. Less dense (faster) to denser (slower) medium For example, air to glass Angle of incidence and angle of refraction are measured from the normal!  Light bends towards the normal.  Angle of refraction is smaller than angle of incidence. Normal Angle of incidence Angle of refraction Refracted ray Incident ray

5. Explanation Use the rolling barrel as an analogy. One end touches the grass first and slows down while the other end rolls with the original speed. As a result, the barrel turns towards the normal. Concrete Grass This end slows down first when it touches the grass. As a result, the barrel turns.

6. Predict How will light bend if it travels from air to water? (Index of refraction of air : almost 1 Index of refraction of water : 1.333 Index of refraction of glass is around 1.5. ) Will the angle of refraction smaller or larger than that in the previous case (air to glass)? Why? Verification by simulation http://www.ps.missouri.edu/rickspage/refract/refracti on.html

7. Denser (slower) to less dense (faster) medium For example, glass to air  Light bends away from the normal.  The angle of refraction is larger than the angle of incidence Glass (slower medium) air (faster medium)

8. Explanation Use the rolling barrel as an analogy. One end touches the concrete ground first and speeds up while the other end rolls with the original speed. As a result, the barrel turns away from the normal. Concrete Grass This end speeds up first when it touches the concrete. As a result, the barrel turns.

9. Predict How will light bend if it travels from water to air? (Index of refraction of air : almost 1 Index of refraction of water : 1.333 Index of refraction of glass is around 1.5. ) Will the angle of refraction smaller or larger than that in the previous case (glass to air)? Why? Verification by simulation http://www.ps.missouri.edu/rickspage/refract/refracti on.html

10. In conclusion Faster medium to slower medium  bends towards normal Slower medium to faster medium  bends away from normal The greater the difference in the index of refraction between the two medium, the more light bends. Question: Is it possible that light travels from one medium to another without changing the direction? Yes, if light strikes the boundary perpendicularly!

11. Light strikes the boundary perpendicularly Can you use the analogy of rolling barrel to explain this? Medium 1 Medium 2 Boundary

12. Exactly how much does light bend? Snell’s law (optional)

13.  How does light bend when it travels from a less dense (faster) to a denser (slower) medium?  How does light bend when it travels from a denser (slower) to a less denser(faster) medium?  Under what condition will light travel from one medium to another without bending?  Can you explain the behavior of light using the analogy of a rolling barrel now?