Transcript Thin Insulator

Exam 3 review.
same rules as prior exams. Mostly covers:
cameras-- lenses, images, focusing, depth of focus, light, etc
digital cameras-- ccd arrays, color perception, color filtering, and
reconstruction
fiber optics-- index of refraction, total internal reflection.
lasers- spontaneous and stimulated emission, population inversion, optical
feedback, why laser light special
Balloons – behavior of gases with changes in temperature, pressure,
volume, ideal gas law, buoyancy force & gravity force and why balloons rise
or not.
Nuclear weapons - behavior of gases with changes in temperature,
pressure, volume, ideal gas law, buoyancy force & gravity force and why
balloons rise or not.
Stabilizing effect of neutrons in the nucleus …
why do you need them?
If only have big bunch of protons,
proton repelling each other a whole
bunch. Like putting a bunch of people
who find each other repulsive in same
room… UNSTABLE SITUATION
Add neutrons then space protons a bit
away from each other, proton repulsion
goes down a bit but still have strong
nuclear binding forces. Like putting a
bunch of neutral people between one’s that
find each other repulsive in same room…
MORE STABLE SITUATION
What is the key process in a laser?
a. An electron stimulating the emission of 2 identical photons
from an atom
b. An electron stimulating the emission of an electron from an
atom to produce 2 identical electrons.
c. A photon stimulating the emission of a photon from an atom
to produce 2 identical photons
d. A photon stimulating the emission of 2 identical electrons
e. An atom emitting a photon spontaneously
Correct answer is c! When photon hits exited atom …
c. second identical photon comes out.
Cloning photons. Amplifying amount of light x 2.
STIMULATED EMISSION
Laser-- Light Amplification by Stimulated Emission of Radiation
method for cloning of photons to produce
LOTS of identical photons of light:
-same direction,
-same wavelength,
-electromagnetic waves all oscillating together.
Requirements: stimulated emission (always have)
population inversion of bunch of atoms (hard)
optical feedback (mirror)
1. absorption of light
photon
atom
electron in higher
energy level
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2. Spontaneous emission of light. Electron jumps down from
upper level, gives off light. Randomly in any direction. Takes some time
for this to happen.
3. Stimulated emission of light. First realized by A. Einstein
Photon hits atom already in higher energy level.
c. second identical photon comes out.
Cloning photons. Amplifying amount of light x 2.
Need population inversion … more atoms in higher energy level than
lower energy to get more light than you put in?
try getting by shining lots of light on atoms.
If turn light way up will get:
a. population inversion with all atoms excited to upper level,
b. no atoms in upper,
c. half the atoms in upper.
Answer is c…
Half in higher energy level, half in lower energy level
… equally likely for photon to hit unexcited atom and be absorbed
… or for photon to hit excited atom and be cause stimulated emission.
Use atoms with 3 energy levels to get population inversion, will give
amplification of red light. If enough atoms in upper level, will lase.
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Happens fast
3
also can kick up by
bashing with electron
Spontaneous emission slow;
Lots of time for stimulated emission
LIGHT to PUMP
Atoms up to level 2
Add mirrors to
build up red light
inside so good
supply for
stimulating
emission
Hot air balloons
What happens when heat air in
balloon?
a. Pressure inside rises so greater than
outside and buoyancy force increases
b. Pressure inside rises so greater than
outside and buoyancy force constant
c. Pressure inside decreases so smaller
than outside and buoyancy force
increase
d. Pressure inside constant so same as
outside and buoyancy force increases
e. Pressure inside constant so same as
outside and buoyancy force constant
Hot air balloons
F buoyancy
Weight
(F gravity)
What happens when heat air in
balloon?
Correct answer is e.
Pressure inside constant so same as
outside
Hot air balloon open at bottom.
So pressure inside will always be
same as outside. As air heated,
some air molecules leave.
and buoyancy force constant because
volume of balloon is constant.
Buoyancy force upwards is due to
air molecules surrounding balloon
hitting outside of balloon. Doesn’t
matter what is in balloon.
Hot air balloon rises because
Buoyancy force upwards greater than weight (Fgravity) downwards
FILM
Center line of lens
If film is placed where yellow dot is in focus, which of dots
will also appear in focus on film?
a. Green dots
b. Blue dots
c. Red dots
d. Both red and blue dots
e. Both blue and green dots
FILM
Center line of lens
Lens equation:
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Object
distance
Image
distance
Focal length
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=Distance+ Distance
to object to image
If film is place where yellow dot is in focus, which series of dots
will appear in focus on film?
a. Green dots
b. Blue dots
c. Red dots
Answer is b. Blue dots! …
Draw rays, each lens has fixed bending power.
Shorter focal length.. More bending power.
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A pixel of the CCD (Charged-coupled
Device) Array
Thin Insulator
N-Type
Energy 
P-Type
semiconductor
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Excess Excess
negative positive
charges charges
Depletion Region
Thin Conductor
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A pixel of the CCD (Charged-coupled
Device) Array
Thin Insulator
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semiconductor
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A pixel of the CCD (Charged-coupled
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Thin Conductor
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Camera can detect red
light but not IR light.
Why not?
a. IR photons have too
little energy
b. IR photons absorbed
by filter on outside
c. Could be a or b.
d. Neither a or b.
A pixel of the CCD (Charged-coupled
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A pixel of the CCD (Charged-coupled
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Thin Insulator
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What will happen to excited
electron?
Answer is b. Move to right.
Attracted to center of Ntype with lots of positive
charge.
A pixel of the CCD (Charged-coupled
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More photons absorbed.
More electrons pile up.
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Thin Conductor
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These e-’s stuck in
upper band. No
empty energy levels
below.
Isolating the pixels of the CCD (Chargedcoupled Device) Array
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Electrons pile up… 1 electron
per photon absorbed.
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positive excess charge (pixel).
After exposure of CCD. Read
out each pixel. Move charges
as a unit to readout.
electron capacitor, measure V created
counter
To capture information about color: put colored filters
in front of each pixel
100 %
transmission
through filter
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if I send in 580 nm (orange) light, what will be fraction that
comes through red filter? a. 100% , b. 80, c. 50, d. 20, e. 0 %
b. 80%
What about through green filter? a. 100% , b. 80, c. 50, d. 20, e. 0 %
c. 50%
What fraction of each orange photon comes through green filter.
d. half the time 0,
a. 0%, b. 50%, c. 100%, d. either 0% or 100%,
half the time 100%
To capture information about color: put colored filters
in front of each pixel
100 %
transmission
through filter
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if I send in 620 nm light into green filter, what will come through will be,
a. a little red light, b. a little green light, c. no light will come through, d. most
of light will come through but it will all be green.
a. red. light does not change color, filter only effects amount that comes
through. Rest of light gets absorbed by filter, turned into heat.