Announcements 10/31/12

1. Announcements 10/31/12 • Prayer • Missing slinkies from: Seth, Ryan, William B, Mike P, Clement • Exam grading—will start right after class today, hopefully done by tomorrow • Term project – progress report due Sat, Nov 10. Grading, out of 10 pts: • Did you submit a progress report on time? • Did your progress report show evidence that you had made significant progress on your project, and that you were on track to complete your project on time? • Was it less than 650 words and in the correct format (text in body of email, partners CC’ed, figures as attachments if needed)? Pearls Before Swine

2. From warmup Extra time on? (nothing in particular) Other comments? These last few sections have been very fun. This section wasn't as interesting for me as others, so I'm in the mindset of "give me the problems so I can get this section over with."

3. Clicker question (review answer): In polarized sunglasses, some of the glare from the sun is eliminated when the sun is directly in front (and above) you. Should the polarizing material be aligned to allow vertical or horizontal electric fields through? vertical horizontal

4. t r Brewster’s angle, review • The Equation • Why is 90 special? “Brewster’s Angle” p-polarization field amplitudes vs q

5. What’s an image? • When you look at it, it looks like there’s an object present at a certain location (but there isn’t, really) • Real • The light rays you see all pass through the location of the image • Virtual • The light rays you see all just seem to be coming from the location of the image

6. Clicker question: • Is the image you see behind a mirror real or virtual? • Real • Virtual How can you ever get a real image to form with a mirror?

7. A Real Image • Use a curved mirror On the advantages of arrows…

8. From warmup What does it mean for a mirror to have a large "radius of curvature"? The mirror, while still curved, it quite flat. If you were to extend it all the way, it would make a gigantic sphere.

9. Clicker question: • What is the focal length of a concave mirror with a radius R? • R • -R • R/2 • -R/2 • R2 Proved in a HW problem

10. From warmup While decorating your Christmas tree you notice that you can see yourself in one of the spherical, reflective ornaments. Is your image real or virtual? How do you know? I think it's virtual. The rays of light aren't actually passing through the point. Virtual, because it appears to be inside the ornament.

11. Demos • Saucer real image or not. Class poll: What kind of image is this? • Real • Virtual • Spherical mirror with hanging ball pendulum

12. Curved mirrors • Not just any curve will work • Focus: • every ray coming in parallel will pass through focus • every ray passing through focus will exit parallel • I will always use f, not R (f=R/2) Fig 36.8 Fig 36.10

13. Where will it “focus”? “paraxial rays” focus useful “third ray”: center of mirror is flat

14. p ho hi f q Similar triangles: Similar triangles: The equation: The equation focus

15. From warmup Will a converging (concave) mirror ever produce a focused image at the focal point? If yes, when? If not, why not? Yes if light comes from an object infinitely far away (so that incoming rays are parallel to the plane of the mirror) (My answer) No, because the object would have to be infinitely far away

16. p ho hi f q Similar triangles Magnification focus Define M: Useful way to calculate: Force M to be negative if image is inverted.

17. Demo • Inverted image in light bulb

18. The equation: “Convex mirror”: curved the other way virtual image!  but f is negative -4.1 cm Numbers: f = -5.5 cm, p = 16.5 cm, q = ? Negative q: means image is in back of mirror

19. Clicker question: • Does a concave (converging) mirror always form a real image? • Yes • No

20. Rest of time: class-designed problem(s) • p = _____ • f = _____ • ray diagram = ? • q = ? • M = ?