1. Announcements 11/2/12 Prayer Slinkies! (Seth, Ryan, William B, Clement) Progress Report due a week from Saturday Pearls Before Swine

2. From warmup Extra time on? a. a.(nothing in particular) Other comments? a. a.Do astronomers have to worry about the fact that air doesn't have an n of exactly 1?

3. Clicker question: A converging lens should be: a. a.convex b. b.concave

4. Convex/converging Lens parallel rays converge to the focal point f if not parallel, they converge (image formed) at a different point at each interface, Snell’s law is satisfied

5. Where will image be formed? focus The equation: Ray diagram just like one for concave mirror, except rays continue to right instead of reflecting back! positive q = right hand side of lens Magnification same:

6. From warmup The mirror eqn and the thin lens eqn look identical. How exactly are they different? a. a.The sign conventions are different, a positive focus means a focus that is "behind" the lens. The same is true of q. b. b.(from my answer) Also--how f is calculated is different. For mirrors, it's simply related to the radius of curvature, but for lenses it relates to the curvature as well as the index of refraction of the lens glass.

7. Clicker quiz Just out of curiosity… have I ever used your warmup answer? a. a.yes b. b.no

8. Concave/diverging Lens parallel rays seem to be coming from the focal point f

9. Diverging lenses virtual image! The equation: (negative f) Negative q: means image on same side of lens as object (virtual)

10. Demos Demo: “Real image or not?” Class poll: What kind of image is this? a. a.Real b. b.Virtual

11. Sign conventions: summary Assuming that the light rays are coming from the left: quantitypositive + negative  p if on the left of the lens/mirror if on the right of the lens/mirror (can only happen in a compound problem) q if on the right of the lens (left side of mirror), means a real image if on the left of the lens (right side of mirror), means a virtual image f if converging: convex lens/concave mirror if diverging: concave lens/convex mirror M if image is right-side upif image is upside-down

12. “Lensmaker’s Eqn” Lens-makers’ eqn:

13. From warmup When you look straight down at an object under water, will it appear to be closer to you or farther away than actuality? Why? a. a.Because you are looking at a flat refracting surface the image of the object forms closer to the surface than the actual object is (figure 36.18). This means the object appears closer to you than it actually is.

14. Clicker Quiz Is that a real or a virtual image? a. a.real b. b.virtual

15. Thick lenses and surfaces Careful with signs!!! (see table 36.2)

16. Clicker question: Can a converging lens ever produce a virtual image? a. a.Yes b. b.No

17. Clicker question: What happens if I cover up the upper half of lens? a. a.Nothing b. b.Upper half of image disappears c. c.Lower half of image disappears d. d.Intensity of image goes down by 50%

18. Clicker question: Can a diverging lens ever produce a real image? a. a.Yes b. b.No

19. Multiple element problems Image of one becomes object of next Worked problem: Find q final, M tot 60 cm15 cm f = 20 cm f = -60 cm Answers: image is 20 cm to right of -60cm lens; M = -0.67