Announcements 11/2/11 Prayer Slinkies!! Exam grading—will start right after class today, hopefully

done by tomorrow Term project – progress report due Sat, Nov 12.

Grading, out of 10 pts: a. Did you submit a progress report on time? b. Did your progress report show evidence that you had

made significant progress on your project, and that you were on track to complete your project on time?

c. Was it less than 650 words and in the correct format (text in body of email, figures as attachments if needed, team members cc’ed)?

Pearls Before Swine

Brewster’s angle, review The Equation

Why is 90 special?p-polarization

20 40 60 80 0.2

0.2

0.4

0.6

0.8

1.0

r

t

field amplitudes vs

1 21

1

tann

n

“Brewster’s Angle”

What’s an image? When you look at it, it looks like there’s an

object present at a certain location (but there isn’t, really)

Reala. The light rays you see all pass through

the location of the image Virtual

a. The light rays you see all just seem to be coming from the location of the image

Reading quiz Is the image you see behind a mirror real or

virtual?a. Realb. Virtual

How can you ever get a real image to form with a mirror?

A Real Image

Use a curved mirror

On the advantages of arrows…

Reading Quiz What is the focal length of a concave

mirror with a radius R?a. Rb. -Rc. R/2d. -R/2e. R2

Proved in a HW problem

Demos Saucer real image or not. Class poll: What

kind of image is this?a. Realb. Virtual

Spherical mirror with hanging ball pendulum

Curved mirrors

Not just any curve will work

Focus: a. every ray coming in parallel will pass through

focusb. every ray passing through focus will exit parallel

I will always use f, not R (f=R/2)

Fig 36.8 Fig 36.10

Where will it “focus”?

focus

useful “third ray”: center of mirror is flat

“paraxial rays”

The equation

focus

p

q

f

hi

ho

Similar triangles:

i

o

h q

h p Similar triangles:

i

i o

h f

h h p

The equation:

1 1 1

p q f

Magnification

focus

p

q

f

hi

ho

Similar triangles

i

o

h q

h p Define M: i

o

hM

h

Force M to be negative if image is inverted.

qM

p

Useful way to calculate:

Demo Inverted image in light bulb

“Convex mirror”: curved the other way

virtual image!The equation:

1 1 1

p q f but f is negative

Numbers: f = -5.5 cm, p = 16.5 cm, q = ? -4.1 cm

Negative q: means image is in back of mirror

Thought question Does a concave (converging) mirror always

form a real image?a. Yesb. No

Rest of time: class-designed problem(s)

p = _____ f = _____

ray diagram = ? q = ? M = ?