Post on 21-Dec-2015
Announcements 11/5/10 Prayer Exam being graded, hopefully done by
Monday Survey about Waves HW problems. Only 7
responses so far. (Thanks!) If you are willing to take the survey, please get your responses in by tonight.
Found PpP book
Quick writing Ralph is confused about the difference
between real and virtual images. What can you say to help him understand?
Convex/converging Lens
parallel rays converge to the focal point
fif not parallel, they converge (image formed) at a different point
at each interface, Snell’s law is
satisfied
Where will image be formed?
focusfocus
The equation:
1 1 1
p q f
Ray diagram just like one for concave mirror, except rays continue to right instead of reflecting back!
positive q = right hand side of lens q
Mp
Magnification same:
Diverging lenses
virtual image!The equation:
1 1 1
p q f (negative f)
Negative q: means image on same side of lens as object (virtual)
Sign conventions: summary Assuming that the light rays are coming from the
left:quantity positive
+negative
p if on the left of the
lens/mirrorif on the right of the
lens/mirror (can only happen in a compound problem)
q if on the right of the lens (left side of mirror), means a real image
if on the left of the lens (right side of mirror), means a virtual image
f if converging: convex lens/concave mirror
if diverging: concave lens/convex mirror
M if image is right-side up if image is upside-down
Reading Quiz When you look straight down at an object
under water, it appears to be ____________ than actuality.
a. closer to youb. farther from you
Thick lenses and surfaces
1 2 2 1n n n n
p q R
1 2
1 1 11n
f R R
Lens-makers’ eqn:
Careful with signs!!! (see table 36.2)
Thought question What happens if I cover up the upper half of
lens?a. Nothingb. Upper half of image disappearsc. Lower half of image disappearsd. Intensity of image goes down by 50%
Multiple element problems Image of one becomes object of next Worked problem: Find qfinal, Mtot
60 cm 15 cm
f = 20 cmf = -60 cm
Answers: image is 20 cm to right of -60cm lens; M = -0.67