Announcements 11/4/11 Prayer Slinkies! HW 28-4 part (d) is canceled Exam update Progress Report due a week from Saturday The three demos from last time Pearls Before Swine

Thought question I look at my image in a shiny round Christmas tree ornament. Which of the following will be true? a. a.The image will be upright (not inverted) and real. b. b.The image will be upright and virtual. c. c.The image will be inverted and real. d. d.The image will be inverted and virtual. e. e.Can’t say… it will depend on where you (the object) are relative to the focus.

Reading Quiz A converging lens should be: a. a.convex b. b.concave

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

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:

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

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

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

Sign conventions: summary Assuming that the light rays are coming from the left: quantitypositive + negative  pif on the left of the lens/mirror if on the right of the lens/mirror (can only happen in a compound problem) qif 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 fif converging: convex lens/concave mirror if diverging: concave lens/convex mirror Mif image is right-side upif image is upside-down

Reading Quiz When you look straight down at an object under water, it appears to be ____________ than actuality. a. a.closer to you b. b.farther from you

Thick lenses and surfaces Lens-makers’ eqn: Careful with signs!!! (see table 36.2)

Thought question Can a converging lens ever produce a virtual image? a. a.Yes b. b.No

Thought 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%

Thought question Can a diverging lens ever produce a real image? a. a.Yes b. b.No

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