1. New Groups and Seating Lab 3: Optics next week, Lab to be posted this weekend. HW 8: Correction problem + paragraph on paper topic/resource. Use this time to work on your paper!!! Due Sunday midnight. Topics: This week and next –Cameras –Digital Cameras

2. The Basic Idea Object Distance Image Distance Object Lens With focal length f Shutter/Iris Film Dark Box

3. Light – A photon particle or a EM wave? When do you need to consider light as PHOTONS: Electronic transition in atom or molecule matches the energy of a photon of the light you are interested in: –Interaction of light with dye molecules, Causes for sunburn, Color of light emitted by LEDs Also need to consider photons if you have so few ‘atom – light’ interactions that you cannot consider average result –Isolated atoms or small clusters of atoms, materials thinner than the wavelength of the light. Absorption of photon Emission of photon Moving along

4. When can you consider light as a LIGHT RAY (EM wave)… good for raindrop, lenses, particles in paint: 3 Criteria: 1.Atoms in material have no electronic transitions near photon energy of the light. Same as saying material is transparent at that wavelength. Glass transparent in visible, not transparent in UV Water is transparent in visible, not in IR Spacing of atoms much, much smaller than wavelength of light, so can just look at average response of ‘atom – light’ interaction 1000s Atoms Per 3. Physical dimensions of material >> wavelength of light, so many, many oscillations between entrance and exit. 2. GLASS

5. Demo of image of object. Camera (or our eye) creates image of object on film (or our retina). What does it mean to make an image? 1) Collecting light coming from object 2) Refocusing the light onto the film (or retina)

6. Looking at distant scenery … : Light rays from a point far away are very nearly parallel by the time they reach your eye

7. Question: Create image of two light sources with lens and cover right half of lens. What will happen on screen? a.Image on left will disappear. b.Image on right will disappear. c.Something else.

8. Question: Create image of two light sources with lens and cover right half of lens. What will happen on screen? c. Something else… Image gets dimmer. Light rays from each light go through all parts of lens so still have image of both, just fewer from each make it to screen.

9. A car changes directions at a concrete/sand interface because the sand slows it down. Same with light. Light bends when it changes speed. Concrete Sand v v

10. Light travels more slowly in glass than in air. Amount of Bend depends on: 1. Change of speed of light at interface. The bigger the change, the more the bend! Index of Refraction (n).For Glass, n=1.5 (light travels 50% slower in glass than air) AND 2. Angle at which light hits surface. The bigger the angle, the more the bend! Light Beam AIR, N=1GLASS, N=1.5 AIR, N=1 In a rectangular slab, light ray straightens out again when it comes back out! Small Reflection

11. Light rays travel straight out in all directions from a point source of light. Which ray of light will have changed direction the most upon exiting the glass? Draw of what you think might happen to each ray. Use car/sand model Glass A C B

12. For an optic to change a light ray’s direction, the sides can’t be parallel. Light rays bent towards each other… CONVERGING LENS. The less parallel the two sides, the more the light ray changes direction. Rays from a single point, converge to a single point and then start diverging again. Put film, Retina here!

13. Focal length – power to bend light Focal length (f) More curved lens is… Less // Entrance and exit surface More bending power Rays converge (come together) shorter distance from the lens. Shorter focal length Focal length (f) Power to bend light (focal length). Figure out where image will be formed. Parallel rays from distance light spot

14. Diverging Lens Bends light rays apart.

15. Camera records real image of object formed by lens: Object Distance (o) Image Distance (i) f f Put Film Here What happens to the image if we move the object closer to the lens? a.Image is same size, same place b.Image is same size and further from lens c.Image is bigger and further from lens d.Image is smaller and closer to lens Do experiment.

16. Answer is c. Move the object closer to the lens makes image is bigger and further away. Lens equation: (o) (i) f f (o) (i) f f Object moves closer… Rays from source diverging rapidly  Lens bends rays toward each other but Lens has set amount of bending power so exit rays converging slowly… Takes more distance to converge to point (o) (i) f f Object moves further away… Just converse of above Distance to object Focal length 1 1 1  Distance to image o f 11 1  i