1. Do Now Grab someone else’s exit ticket from yesterday and do their problem. Use their work as a reference point ONLY. You should show all of your own work. If you think they did their problem incorrectly, double check first & then ask me.

2. Today’s Agenda 5 min Do Now 5 min Important Dates 30 min Snell’s Law Review 20 min Total Internal Reflection

3. Today’s Agenda 5 min Do Now 5 min Important Dates 30 min Snell’s Law Review 20 min Total Internal Reflection

4. Important Dates and Reminders Monthly News Projects Past Due New Homework Schedule  You will receive homework on TUESDAYS (yesterday)  Homework will be due on THURSDAYS (tomorrow) Quiz Retakes All Week Physics Photo Projects Due Fri. May 3 rd Prom Tickets On Sale Until Next Monday!  Tickets are sold in lunch ONLY.

5. Today’s Agenda 5 min Do Now 5 min Important Dates 30 min Snell’s Law Review 20 min Total Internal Reflection

6. Reflection & Refraction Reflection: How light bounces off a surface  Angle of reflection, θ’ 1, equal to angle of incidence Refraction: How light bends at the boundary between two media  Angle of refraction, θ 2, depends on the properties of the medium

7. THE INDEX AFFECTS THE ANGLE THAT LIGHT WILL BEND AT WHICH SHOWS THAT THE SPEED OF LIGHT IS CHANGING IN DIFFERENT MEDIA Index of Refraction

8. SNELL ’ S LAW Where n is the index of refraction

9. Review Problem An incident ray in air (n=1.0) strikes an unknown material at an angle of 45°. The angle of refraction is 70°. What is the index of refraction (n) of the unknown material?

10. Review Problem An incident ray in water (n=1.33) is approaching the boundary with glass (n=1.52) at an angle of incidence of 48°. Calculate the angle of refraction. Draw the refracted ray on the diagram.

11. Review Problem An incident ray in air (n=1.0) is approaching the boundary with diamond (n=2.52). If the angle of refraction was 15°, calculate what the angle of incidence was.

12. Review Problem An incident ray starts in an unknown material and strikes water (n=1.33) at an angle of 55°. The angle of refraction is 25°. What is the index of refraction (n) of the unknown material?

13. Step-Up Problem The diagram shows a ray of light traveling through air (n=1.0) towards a layer of linseed oil (n = 1.50) resting on top of water (n=1.33). The light ray strikes the linseed oil at an angle of incidence of 55°. a. Determine the angle of refraction at the air- linseed oil boundary.  Do this is a regular Snell’s Law problem using air & linseed oil

14. Step-Up Problem The diagram shows a ray of light traveling through air (n=1.0) towards a layer of linseed oil (n = 1.50) resting on top of water (n=1.33). The light ray strikes the linseed oil at an angle of incidence of 55°. b. Determine the angle of refraction at the linseed oil-water boundary  Must use the angle of refraction ( θ 2 ) that you found in the previous problem as the angle of incidence (θ 1 ) for this problem

15. Questions???

16. Today’s Agenda 5 min Do Now 5 min Important Dates 30 min Snell’s Law Review 20 min Total Internal Reflection

17. Total internal reflection happens when light tries to go from a medium with a high index of refraction to one with a lower index of refraction  Ray 5 shows internal reflection Total Internal Reflection

18. FOR THIS TO OCCUR, YOUR ANGLE OF INCIDENCE WOULD HAVE TO BE GREATER THAN SOMETHING CALLED THE CRITICAL ANGLE Total Internal Reflection

19. A particular angle of incidence will give you an angle of refraction of 90°  This angle of incidence is called the critical angle Critical Angle

20. Critical Angle vs. Total Internal Reflection

21. Critical Angle For angles of incidence greater than the critical angle, the beam is entirely reflected at the boundary  This ray obeys the Law of Reflection ONLY since there is no refraction that happens! Total internal reflection happens when light tries to go from a medium with a high index of refraction to one with a lower index of refraction

22. Solving Critical Angle Problems The light has to be moving from the medium with a larger index of refraction to the medium of a smaller index of refraction. Example: Calculate the critical angle at the boundary for ethanol (n=1.36) and air (n=1.0).  What is the direction that light would travel?  Which angle is 90 degrees?  Setup the problem.  Solve the problem.

23. Guided Practice Think-Pair-Share Calculate the critical angle at the boundary of air (n=1.0) and glass (n=1.52).  Determine what direction light would travel.  Determine which angle is 90 degrees.  Setup the problem.  Solve.

24. Guided Practice Teach-A-Friend Calculate the critical angle at the boundary of water (n=1.33) and glass (n=1.52).  Determine what direction light would travel.  Determine which angle is 90 degrees.  Setup the problem.  Solve.

25. Independent Practice Calculate the critical angle at the boundary of diamond (n=2.42) and glass (n=1.52).