1. Chapter 15.1 Announcements:
Homework 15.1: due Tuesday, April 27, in class (Nguyen)
Exercises: 1, 2, 3, 5, 7, 8, 10, 11, 12, 13, 15
Problems: 1, 2, 4, 5
All grades will continue to be posted at:
Listed by last four digits of student ID
Final exam (cumulative): May 4, 2-5 pm
Practices test will be posted
We’ll now cover only parts of each chapter (let me know if you want me to cover something that is not on the list and that interests you):
5.1 Balloons
7.1 Woodstoves
9.1 Clocks
9.2 Musical Instruments
10.3 Flashlights
11. Household Magnets & Electric Motor
11.2 Electric Power Distribution
15.1. Optics, Cameras, Lenses
16.1 Nuclear Weapons

2. Chapter 15.1: Light, optics, cameras, lenses
Demos and Objects
Concepts
light and lenses
camera
eye
Light
lenses bend light
focal point
cameras
object distance
image distance
focal length
lens equation!
film
aperture
depth of focus

3. Light from an Object
An illuminated object reflects or scatters light (sends out light)
You see object via this reflected or scattered light
The object’s light forms diffuse illumination
You can’t tell what object looks like from this diffuse illumination
Demonstration: Cast Light on Ground Glass Screen
… but we see object

4. Lenses Types of lenses: Most important simple optical device
Lenses bend light
Lenses can form images of objects
Used in glasses, cameras, telescopes, binoculars, microscopes, …
Converging lenses: thicker in the middle than the outside
Diverging lenses: Thinner in the middle than the outside

5. Parallel rays incident on converging lens
Light rays get refracted by a lens, that is: light gets bent by a lens.
If the rays come in parallel to the principal axis (object at infinity), they will be focused in the focal point.
focal length f
focal length is the same on both sides, even if lens is not symmetric.
Parallel rays coming in, focus on the focal plane

6. Parallel rays incident on converging and diverging lenses
Any lens that is thicker in the center than at the edges will make parallel rays converge to a point and is called a converging lens.
Any lenses that are thinner in the center are called diverging lenses, because they make parallel rays diverge.
Focal point of diverging lens: Point were diverging rays seem to be coming from.

7. Converging Lenses A converging lens uses refraction to bend light rays
Light rays converge after passing a converging lens
Rays from a common point on an object converge to a common point on far side of the converging lens
Demonstration: Elmo Optics Forming Real Image
Demonstration: Cast Real Image on Ground Glass Screen

8. Real Images An image forms in space on far side of lens
The image is a pattern of light in space that exactly resembles the object, except for size and orientation
The image is “real” – you can put your hand in it and you can capture it on a screen (eye, camera).
Demonstration: Show That Real Image Exists With or Without Ground Glass Screen
Demonstration: Use Focus of Camera to Show that Real Image is at a Particular Location in Space

9. i-clicker-1
A magnifying glass held in sunlight forms a round spot that can burn paper. What spot(s) will form if you hold that lens in light from the lamps overhead?
A round spot
A square spot
Spots that look exactly like the overhead lamps
Round spots arranged like the overhead lamps

10. Lenses and Film Eyes and Retina
Capturing image and
leading up to lens equation
Lenses and Film Eyes and Retina
Film records the pattern of light it’s exposed to
If you put film in a real image, it will record a pattern of light resembling the object
For a good photograph, the real image should be sharply focused on the film and have the right size
Film or retina

11. Focusing Light reaching the lens from an object is diverging
Capturing image and
leading up to lens equation
Focusing
Light reaching the lens from an object is diverging
The nearer the object, the more its light diverges
Converging lens has trouble with diverging light
Real image of nearby object forms farther from lens
Real image of distant object forms closer to lens
Demonstration: Real Image of Three Lamps at Different Distances

12. Focal Length Focal length measures the lens’ converging ability
Long focal length: weak convergence, long image distance
Short focal length: strong convergence, short image distance
The larger the object distance, the bigger the image
Long focal length: big images
Short focal length: small images
Demonstration: Show Real Image Size with Various Focal Length Lenses and Lamps
Capturing image and
leading up to lens equation

13. Ray tracing for converging lens to find the image created by the lens
Ray 1 leaves top point on object going parallel to the axis, then goes through focal point.
Ray 2 passes through F’, therefore it is parallel to the axis beyond the lens
Ray 3 passes straight through the center of the lens.

14. Capturing image and
lens equation
The lens equation ho hi f o i

15. The lens equation: Magnification: Draw a ray diagram
Lens equation and
magnification
The lens equation:
Magnification:
Draw a ray diagram
Solve for unknowns in the lens equation and magnification. Remember reciprocals
The height of the image, hi is positive if the image is upright, and negative if the image is inverted relative to the object (ho is always positive).

16. i-clicker-2; -3 hi Image formed by a converging lens.
You place a 7.6 cm high flower 1.00 m from the lens of a camera (focal length 5.0 cm).
What is the position (image distance) if the image
What is the size of the image on the film of the camera.
1A cm
1B cm
1C cm
1D cm
1E cm
1A. 1 mm
1B. 2 mm
1C 3 mm
1D. 4 mm
1E mm
ho =
7.6 cm hi
f = 5 cm
o = 100 cm
i = ?

17. Lens Diameter and focusing
Larger lens
converges more light
brighter image
focus becomes more critical
less depth of focus
Smaller lens
dimmer image
focus becomes less critical
more depth of focus
Demonstration: Show Effects of an Aperture on Depth of Focus

18. i-clicker-4
A disposable film camera has no focus adjustment. To produce sharp photographs that are properly exposed, it needs a
large diameter lens and low sensitivity film.
small diameter lens and low sensitivity film.
large diameter lens and high sensitivity film.
small diameter lens and high sensitivity film.

19. Aperture and f-number Aperture characterizes the diameter of the lens
F-number is lens focal length (say 35 mm) divided by lens diameter (adjusted by aperture).
Large f-number (22 or so on lens).
Dim image
Large depth of field/focus (focus is forgiving)
Small f-number (3.5 or so on lens).
Bright image
Small depth of field/focus (focus is critical)

20. A B i-clicker-5 Which photograph was taken with a larger aperture?
Clear focal plane, short focal depth, focus is crisp
No clear focal plane, very long focal depth, focus is not crisp