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: a. a.Did you submit a progress report on time? b. b.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? c. c.Was it less than 650 words and in the correct format (text in body of , partners CC’ed, figures as attachments if needed)? Pearls Before Swine

From warmup Extra time on? a. a.(nothing in particular) Other comments? a. a.These last few sections have been very fun. b. b.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."

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? a. a.vertical b. b.horizontal

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

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 a. a.The light rays you see all pass through the location of the image Virtual a. a.The light rays you see all just seem to be coming from the location of the image

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

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

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

Clicker question: What is the focal length of a concave mirror with a radius R? a. a.R b. b.-R c. c.R/2 d. d.-R/2 e. e.R 2 Proved in a HW problem

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? a. a.I think it's virtual. The rays of light aren't actually passing through the point. b. b.Virtual, because it appears to be inside the ornament.

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

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

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

The equation focus p q f hihi hoho Similar triangles: The equation:

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

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

Demo Inverted image in light bulb

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

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

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