Announcements 3/11/11 Prayer More Slinkies? HW & Lab with no CID Exam going on until tomorrow Lab 7 starts tomorrow Term project – progress report due Sat, Mar 19. 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 your proposal less than 650 words and in the correct format (text in body of email, figures as attachments if needed)?
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Announcements 3/11/11 Prayer More Slinkies? HW & Lab with no CID Exam going on until tomorrow Lab 7 starts tomorrow Term project – progress report due Sat, Mar 19.
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 your proposal less than 650 words and in the correct format (text in body of email, figures as attachments if needed)?
Brewster’s angle, review The Equation
The Explanation
Sunglasses
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”
Thought question
If you send an unpolarized beam at a piece of glass at Brewster’s angle, what happens?
a. The reflected beam is partially polarizedb. The reflected beam is completely polarizedc. The transmitted beam is partially polarizedd. The transmitted beam is completely
polarizede. More than one of the above
What’s an image? When you look at it, it looks like there’s an
object present (but there isn’t, really) Real
a. The light rays you see are all coming from the location of the image
Virtuala. 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 = ?
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