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Announcements 11/8/10

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- Prayer
- Exam 2 graded: median score 79 (after 2 pt curve)
- Found PpP book
- Still missing slinkies from:
- Stephen Grant
- Ty Beus
- Jon Mortensen
- Chris Read
- Roger Brown
- Tess Larson (I think she dropped; does anyone know her?)

- Draw the ray diagram for this situation: Converging lens, f = 20 cm, p = 80 cm

- Draw the ray diagram for this other situation: Converging lens, f = 20 cm, p = 15 cm

- Draw the ray diagram for this third situation: Diverging lens, f = -20 cm, p = 5 cm

- What’s the term used to refer to rays failing to focus because a lens is shaped incorrectly?
- elliptical aberration
- hyperbolic aberration
- parabolic aberration
- spherical aberration

Credit: the next several slides were produced by Dr. Durfee

Lens-makers’ eqn:

- Red light coming from O produces an image at I. Where will blue light coming from O form an image?
- same place
- closer to the lens
- farther from lens

ChromaticAberration

- Simplest picture
- What if you leave out the lens?
- What’s a pinhole camera?

- What is the f-number of a lens?
- The focal length in meters
- The focal length in inches
- One over the focal length in meters
- The focal length divided by the diameter of the lens
- The focal length divided by 25 cm

q

- How does the f-number of a lens relate to the half-angle of the “light cone” formed by parallel light entering the lens?

- Which has the higher f-number?
- What’s the advantage of one over the other?

- If you have trouble seeing things far away but can see close objects well, you are “near-sighted”. What kind of lenses do you need in your glasses?
- Converging lenses
- Diverging lenses

- Near point: how close can you see things comfortably
- Regular person: np 25 cm
- Farsighted person: np = much larger

- Far point: how far away can you focus on things
- Regular person: fp = infinity
- Nearsighted person: fp = much smaller
- For me, my fp 1 m (right eye), 0.5 m (left eye)