Announcements 11/2/11 Prayer Slinkies!! Exam grading—will start right after class today, hopefully done by tomorrow Term project – progress report due Sat, Nov 12. 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 , figures as attachments if needed, team members cc’ed)? Pearls Before Swine

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

Reading quiz 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…

Reading Quiz 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

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:

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

Thought 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 = ?