announcements 11/2/12 prayer slinkies! (seth, ryan, william b, clement) progress report due a week...
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Announcements 11/2/12 Prayer Slinkies! (Seth, Ryan, William B, Clement) Progress Report due a week from Saturday
PearlsBeforeSwine
From warmup
Extra time on?a.(nothing in particular)
Other comments?a.Do astronomers have to worry about
the fact that air doesn't have an n of exactly 1?
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:
From warmup
The mirror eqn and the thin lens eqn look identical. How exactly are they different?
a.The sign conventions are different, a positive focus means a focus that is "behind" the lens. The same is true of q.
b.(from my answer) Also--how f is calculated is different. For mirrors, it's simply related to the radius of curvature, but for lenses it relates to the curvature as well as the index of refraction of the lens glass.
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
From warmup When you look straight
down at an object under water, will it appear to be closer to you or farther away than actuality? Why?
a. Because you are looking at a flat refracting surface the image of the object forms closer to the surface than the actual object is (figure 36.18). This means the object appears closer to you than it actually is.
Clicker 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%
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