Three Kits for CMDITR Outreach
Overview
The demo kits are meant to provide support for quick, engaging classroom or public
presentations. The initial kits contain materials for demo presentations not necessarily enough
for full-class, hands-on activities. The presenter guide provides a flexible “script” explaining how
to do the demos, what points to make and how to relate it to the CMDITR focus. Presenters use
these as starting points or accents to their own unique presentation that is geared to the
audience and venue. The table below maps the topics approximately to grades. Higher level
demos might be appropriate as the “gee whiz” demos for earlier grades without getting into the
conceptual explanation. At the same time a solar car could be an appropriate conversation
piece when talking about a higher level topic.
KIT
Optics and lasers
Elementary Topics
Color mixingLight goes in straight
line
Middle/Public Topics
Lenses/optics
Reflection, refraction,
absorption,
luminescence
High School Topics
Polarization
Diffractionwavelength
Photovoltaics
Solar car
Rechargeable
batteries
Angle/area/ distance
dependence
Circuits – series and
parallel
Types of cells
Total efficiency
Voltage/current
curves
Raspberry Cell
Color Absorption
Internal reflection
Sugar water bending
light
Tyndal effectattenuation
Control light with
polarization
Interference
Index of refraction
Fiber networking
Telecommunications Light carries
information
Optical fiber
Water stream demo
These kits were designed by the Center for Materials and Devices for Information Technology
Research (CMDITR) an STC Program of the National Science Foundation No. DMR 0120967.
http://STC-MDITR.ORG
Education Standards
Science classroom time is packed full and teachers have many specific educational objectives
that are dictated by their districts and states. One key to being welcomed to the classroom is to
relate your presentation to specific content they have to cover anyway. Even if your specific
science is not covered you can switch the activity format to address general process skills such
as observation, hypothesizing, designing an experiment and interpreting results. Careers and
the connection between science, technology and society are also hooks that tie into must
curricula.
Overview Page 1 of 2
To learn what is taught at various grade levels check the National Science Education
Standards, AAAS Project 2061 and the links to state Science below.
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http://www.nap.edu/openbook.php?record_id=4962&page=104 National Science
Education Standards - Grade level Content
http://www.project2061.org/publications/bsl/online/index.php?chapter=4 AAAS 2061
Benchmarks - The Physical Setting
http://www.education-world.com/standards/state/toc/index.shtml Education World State
Standards Links
http://www.mcrel.org/compendium/SubjectTopics.asp?SubjectID=2 McREL Content
Knowledge
http://dev.nsta.org/ssc/ National Science Teachers Association- Science Scope and
Coordination
More Hands On Demos and Activity Ideas
 http://depts.washington.edu/cmditr/media/Educ_demo_suppliers.docx List of suppliers
for education kit materials
 http://www.hands-on-optics.org/resources/ HANDS ON OPTICS- (from OSA, SPIE and
NOA0
 http://projectsol.aps.com/inside/inside_pv.asp APS Project Sol- Animation explains
silicon solar solar cells
 http://www.solideas.com/solrcell/cellkit.html Solar Cell Kit-How to build your own solar
cell
 http://spie.org/etop/2007/etop07k12V.pdf Innovative Methods to Teach Optics in the
Grade 5- (including jello optics)
 http://www.exploratorium.edu/snacks/index.html Exploratorium - Snacks are simple
demo ideas - this is the premier organization for hands-on demos and learning
 http://ice.chem.wisc.edu/Catalog/SciKits.htm#Anchor-Optical-13405 Institute for
Chemical Education- Source for kits
 http://mrsec.wisc.edu/Edetc/nanolab/index.html Video labs in Nanotechnology from Univ.
Wisconsin MRSEC
 http://www.optics.rochester.edu/workgroups/berger/EDay/EDay_Writeups.html
Rochester Optics demonstrations for Eday
 http://www.osa.org/educationresources/youtheducation/classroommaterials/default.aspx
OSA classroom materials including the Optics Suitcase
Overview Page 2 of 2
Basic Light and Optics
The purpose of this kit is to introduce students to the basic properties of light such as color,
straight beams, reflection, refraction and polarization. Each of these phenomena can be
presented in a “discovery” mode in which students related their current knowledge by guessing
what will happen. At a higher level some of the phenomena can be explained with formulas and
confirmed with measurements. Following each demo description are ideas of how to tie the
demo into the CMDITR science.
Key Concepts and Demos
1) Diffraction Grating
White light is composed of many colors. Pass around the diffraction grating. There is
a loose grating as well as one in the color filter paddle set. Have them describe what
they see. Are the colors the same for any light you look at? The diffraction grating is able
to split white light into colors that make it up. (The diffraction grating works because of
constructive and destructive interference, but this is higher level concept.) Students may
be able to notice that the colors difference between an incandescent bulb, and LED and
fluorescent bulb shown below. Connect this idea to other sources of rainbows colors
such as a rainbow (reflection and dispersion within a drop of water), oil sheen on water
(interference between nanolayers), or prisms (transmission and dispersion). You could
also use the equilateral prism of from the prism set to create a rainbow by refraction.
Research Connection: Sunlight is composed of many colors. To be efficient solar
cells need to be able to capture all colors. Organic LED light sources can be
designed to provide specific colors.
Basic Optics Kit Page 1 of 12
2) Additive Color Mixing
When red, green and blue are added together they produce white. Turn on a white
flashlight. Ask student what colors they see? Say yes to all colors that student answer.
Pass out the color flashlights. These produce red, green and blue light. What happens
when two or more colors of light are combined? By focusing all three colors to one point
a white light is created.
Research Connection: An RGB monitor has tiny red, green and blue dots. All colors
including white can be made by mixing these three colors. CMDITR research with
organic light emitting diodes has led to OLED displays which use thousands of red,
green and blue lights to make all the points on the display.
Basic Optics Kit Page 2 of 12
3) Color filters
Light can be absorbed. Ask students what they know about color.
a. Pass out colored filter samples and have students look at the room. Which color
filter makes the light of a certain color go away? Colored filters absorb different
colors and let other colors through. The deluxe filter paddle also has a polarizing
filter and a diffraction grating.
b. Ask which color paints are mixed together to make other colors. Is it possible to
make white paint by mixing colored paints? (No this is because each color
absorbs another part of the spectrum. If you added enough colors together
eventually to would absorb all the light making black.) Have student pick three
colors from the sample pack that when combined makes black or grey. If an
organic solar cell appears red colored what does tell you about its absorption
spectrum? The color of reflected light from a material represents the color of light
that is not absorbed.
c. Print out the “red reveal” hidden message sheets. Ask student to find a filter that
reveals the hidden message. The red filter will mask all the colors that are similar
to red in the picture. This leaves only the cyan layer that shows up as black
because no light of this color can pass through the red filter.
Research Connection: Solar panels are black because they absorb many colors. We
are trying to design new materials that can capture solar energy and convert the energy
to electricity. It would might pretty but it might not work as well as one that appears
black. Why?
Basic Optics Kit Page 3 of 12
Basic Optics Kit Page 4 of 12
4) Spectroscope
The color of light can be described by wavelength. You
may not notice it but every light has its own unique color. A
spectroscope is an instrument that lets you measure all the
colors present in a light source.
a. Point the spectroscope at a fluorescent light and
look through the hole on the end with the diffraction
grating. Notice the green line that appears at the
5450 mark. Fluorescent bulbs are actually a little bit
green. Some street lights are blue or even orange.
This color depends on the chemistry of the materials used in the bulb.
b. Now place a color filter #89 that only transmits color in the green part of the
spectrum. Notice that the red line disappears from the fluorescent spectrum. Try
using other filters to isolated different lines. What rule can you come up with
about what color filters do to the full color spectrum of light? ( A color filter blocks
all colors except for the color it appears to be. Similarly reflective colors absorb
all light except for the color they can be observed to reflect)
Research Connection: LEDs have distinct colors. Scientists and engineers are
working to make LEDs that have light with the full spectrum of sunlight so colors look
right. Other applications require LEDs with a very specific wavelength to match the
material they must pass through such as plastic screens or fiber optics.
Research Connection: We use instruments like the spectroscope to measure the
light absorbed by chemicals we produce and to measure the light the color produce
when they stimulated with lasers and electricity.
Basic Optics Kit Page 5 of 12
5) UV sensitive beads
Some portions of the electromagnetic spectrum are invisible. Point out the colors
on the electromagnetic spectrum chart and show that some types of radiation are not
visible. Pass out some UV beads. These are photochromic beads which change color in
the presence of UV light but revert to white in the dark or in incandescent room light. Ask
students if all light is visible. Have them place the beads in various places around the
classroom under lights, in the dark and in the sun. Explain that UV light is invisible but
very powerful and is the cause of sun burns.
As an extension you could apply UV skin sunblock to a bead and see how effective it is
in blocking UV rays.
Research Connection: UV light is damaging to the body. It is also damaging to
organic chemicals that we use in our solar cells. One of the challenges is to make
design chemicals that do not break down in the presence of UV light.
Basic Optics Kit Page 6 of 12
6) Glow Paper
Some materials absorb light and then continue to emit it over time. Some colors of
light do not have enough energy to excite these substances.
a. Turn off the lights in the room. Expose the sheet to light for an instant. Point out
that the sheet glows for an instant and then goes away. A phosphorescent
material gives off light for a time after the light that excites it is turned off.
b. Use the three colored flashlights, the white flashlight,
daylight, colored filters, and the red laser to stimulate the
glow-in-the dark paper. Red light should not be able to
make it glow even though the laser pointer is very intense.
Distinguish between the intensity of light which can be
thought of photon flux or wave amplitude and the energy
level of light which is dictated by the frequency or
wavelength. This is because the chemical in the paper
requires a minimum energy of light in order to excite its electrons to a higher
energy level. Once the higher level is reached the energy slowly decays back to
the ground state emitting light that is observed as glowing phosphorescence.
Also notice that the phosphorescence is a slow phenomena.
Research Connection: We attempt to design organic chemicals that are tuned to
absorb in the range of light that is desired for a given purpose.
Basic Optics Kit Page 7 of 12
7) Quantum Dots Solutions
Materials can be made that designed that absorb and emit radiation at specific
wavelengths. These vials contain extremely small 25nm particles of cadmium selenium that have been
grown to specific sizes because of their light absorbing
qualities. These particles exhibit fluorescence; they
absorb light at one color and emit light at a different
wavelength. In the visible spectrum they absorb and
emit yellow and pale red. They absorb ultraviolet and
fluoresce in green, red and orange.
a. Examine the vials in regular light. Predict what
color the vials will appear under UV light.
b. Expose the vials to UV light
Research Connection: It is possible to use quantum
dots as a light antenna to absorb light and pass energy
to another chemical. Some quantum dots for example could be used to trap infrared (IR )
light which would help solar cells work on cloudy days when IR passes through the
clouds but visible light is mostly blocked.
8) Electroluminescent Panel
Electricity can be used to excite a material and
make it emit light. Electroluminescent panels
have a transparent conductor layer, a layer of
phosphor and a metal back electrode. When the
front and back electrode are energized with a high
frequency current the phosphor in between is
stimulated and emits light.
Research Connection: Electroluminescent panels are similar to the structure of
Organic Light Emitting Diodes (OLEDs). Instead of a layer of phosphor the OLED
contains an organic chemical that emits light after being excited with electricity. The
organic chemicals can be tuned to get specific colors. OLEDs are now used for flat
displays and televisions.
9) Laser pointer
Basic Optics Kit Page 8 of 12
Light goes in a straight line until it interacts with matter. All light sources produce
beams of light. Lighting usually produces many beams going many
directions.
a. A laser produces a very bright, focused beam. Use the laser
show the path of a light beam. Laser light is used to guide
rockets, in surveying or carpentry to line things up, or even to
guide farm machinery. Place the laser along a flat surface such
as the floor or table and show that it is not affected by gravity.
b. Fill the plastic tub with water and add some powdered milk
powder to make the light beam visible. A tub of clear gelatin can also be used for
this demonstration.
10) Mirrors and lasers
Light can be reflected. First ask what kinds of
objects reflect light. Test the theories about what will
reflect by pointing the laser at the objects that are
suggested. They should be able to describe the
quality of shiny, glassy or metallic being needed for
mirrors.
a. Place a mirror on edge on the table with a
protractor in front of it. Place the cylinder lens
end tip on the laser so that it produces flat
line instead of a dot. Orient the line so it is
vertical (with the cylindrical lens horizontal).
This will make it easier to see the light ray and its reflection on the table. Use the
protractor to measure the angle of light coming in (angle of incidence) and the
angle of reflection. What is the rule for this? (the angle of incidence equals the
angle of reflection)
b. Challenge: what arrangement of mirrors would be needed to reflect a laser beam
into a complete circle? Optical fiber has smooth surfaces and narrow diameter.
Light reflects inside the tube until it emerges from the end. This is called total
internal reflection.
Research Connection: We do many experiments with lasers that pass through many
lenses, filters and sensors on a special optics table. We move the laser beam around the
table using mirrors and large optical fibers. Some lasers are so powerful they can burn a
hole in wood if the beam is absorbed. Mirrors can reflect this light without getting hot at
all.
11) Refraction with grow cubes and prisms
Light can be refracted.
a. One day before the demonstration place several of the optic grow cubes into
water in a plastic bag. Each cube will expand into a 3 cm, optically clear cube.
Use the single edge razor to cut the cube into various shapes used in optics.
Alternatively cast a sheet of clear gelatin using three times as much gelatin as is
Basic Optics Kit Page 9 of 12
called for on the recipe. Use the laser pointer to show how lenses and prisms
work. Try making a convex lens, a concave lens, an equilateral prism, a fiber
optic tube, a periscope with right angle prisms.
b. Use the acrylic prism set to demonstrate various optics phenomena. If possible
use two lasers to show parallel beams. The equilateral prism produces a rainbow
in sunlight.
c.
Research Connection: We use lenses to focus light to a point for experiments, or to
make a wide parallel beam. Prisms are used to separate light into the color spectrum
and then isolate particular color bands in instruments such as the monochromator.
Basic Optics Kit Page 10 of 12
12) Polarizing Filters
Light waves can be random or polarized in one direction. Polarized materials only
allow light with a certain orientation to pass through.
a. Have two students hold the nylon rope and generate a wave in the crossways
direction. Place two straight back chairs back to back on either side of the rope
so that it’s horizontal movement is limited. The waves will be dampened. Ask the
students to generate a wave in the up and down direction. This will pass through
between the chairs. This how a polarized light is blocked or passed through a
polarizing filter.
b. Use the polarizing filters to show that light from a laser or from an LCD monitor
can be almost completely blocked as the filter is rotated. Two filters can be used
to block non polarized light.
c. Clear materials such as plastics can change the polarity of light when they are
under stress because their molecules get aligned in a certain way by forces. If
you place a clear plastic spoon between two polarizing filters or between an LCD
monitor (a polarized light source) and a polarizing filter you can see rainbow
colored patches where light is being blocked or refracted in response to stresses
in the material.
Research Connection: Liquid crystal displays have a polarized light source. The
liquid crystal chemicals can be rearranged when electricity is applied to change the
way they polarize light and thus let certain light pass through under the red, green
and blue cells. This property can be used to control light in fiber networks and
computers.
Research Connection: CMDITR is creating new organic materials that can change
their polarization in an electric field or when light of specific wavelength is provided.
Basic Optics Kit Page 11 of 12
13) Lasers and diffraction grating
Lasers light is coherent and a precise wavelength. Place a diffraction grating in front
of the laser pointer. There will be three dots, one for straight transmission and two
diffracted dots on either side. Compare this to the pattern that appears from looking at a
fluorescent bulb with a diffraction grating.
Research Connection: Researchers pick lasers that have precisely the wavelength
they need for their experiments. For example most optical fiber communications
operate at 850nm or 1300 nm wavelength.
14) Advanced Laser experiments See experiments 6, 7, 8 of the laser kit
Sources
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http://www.i-fiberoptics.com/laser-kits-projects-detail.php?id=2240 $51 Laser pointer
education kit class II red laser pointer
http://www.arborsci.com/detail.aspx?ID=1428 grow lens cubes (100s) $8 (clear gel to
play with lens shapes)
http://scientificsonline.com/product.asp_Q_pn_E_3053471 Acrylic prisms set $34
http://scientificsonline.com/product.asp?pn=3082363 UV beads $7.95
http://www.arborsci.com/detail.aspx?ID=894 Filter paddle samples 2 x $12
http://www.officedepot.com/catalog/vendorRouter.do?configurableItemType=NORWOO
D&id=976090 White LED flashlights 3 x $5
http://www.arborsci.com/detail.aspx?ID=380 Fog in a can $16.95
http://www.arborsci.com/detail.aspx?ID=395 slide mounted polarizing filters( 50) $33
http://www.arborsci.com/detail.aspx?ID=37 6 gel color filter pack $12
http://www.arborsci.com/detail.aspx?ID=928 Phosphor Glow Paper $3.95
http://www.arborsci.com/detail.aspx?ID=319 Adventures in fiber optics kit $44.
http://www.glowhut.com/a6-size-electroluminescent-light-with-9v-invert69.html EL light
with inverter $29
Basic Optics Kit Page 12 of 12
Photovoltaics
Photovoltaics (PV) or solar cells are one of the most promising sources for renewable electrical
energy. The first generation cells were made from silicon crystals like those used computer
semiconductor chips. These are efficient but very expensive. Silicon PV were first widely used
where the cost of wiring to the grid was impractical such as in satellites or to power remote
sensors along pipelines or railway tracks. Materials research and improved manufacturing
techniques have brought the price down to where they are beginning to become practical for
home energy systems. Plastic solar cells that use organic chemicals instead of silicon may be
the next breakthrough. These demos show some basic devices and engage students in
quantifying their performance and considering how basic science relates to engineering design.
Key Concepts and Demos
1) Solar Car - Solar battery charger – (motor - LED)
Solar energy can be converted to electrical energy using a solar cell. Demonstrate
the solar car, the motor and rotor, and solar battery charger. Place the solar car in the full
sun. What happens when the car passes into the shade? Demonstrate that the small
silicon cell doesn’t generate enough energy to power the single LED but the larger
amorphous silicon panel can power the light, even in indirect sunlight. Compare the solar
electricity to power from a battery. See if they know about batteries polarity. Predict what
would happen to the motor if you switch the leads to the solar cell. Reverse the polarity
and the disc on the motor will rotate in the opposite direction.
Research Connection: CMDITR is building a new kind of solar cell that uses an organic
chemicals to trap light and then transfer electrons to conductive layers.
Photovoltaics Kit Page 1 of 19
2) Types of solar cells.
There are several kinds of solar cells which differ power, cost, durability, and
preferred applications. Demonstrate the various types of solar cells in the kit by
connecting them to a motor, voltmeter or LED. For ease of desktop display we have
prepared self supporting mini-displays on which 1-3 cells can be mounted. The dangling
clip leads can be connected to devices and configured in series or parallel circuits.
a. Single crystal and poly crystalline silicon cell.
The smaller cells in the kit are rated .45 volts and
400ma. Crystalline silicon solar cells (c-Si) can
have efficiencies from 10-12%. They are produced
from ingots of solid silicon and are rigid. These are
the cells that most often used in space station
where power density and durability are most
important.
b. Amorphous silicon battery charger. The panel is
rated 7.2 volt / 200ma and has diode built into the
circuit to prevent battery discharge into the panel
when it is dark. Amorphous silicon is made by
depositing an extremely thin layer of silicon on a
conductive polymer. As a result the panel is flexible.
(a-Si) Amorphous silicon has a comparatively low
6% efficiency because the silicon is poorly
organized creating barriers to charge movement but
it makes up for this with a lower cost and ease of manufacturing.
c. Copper indium selenide (CIS) CIS and Copper indium gallium
selenide cells (CIGS) have 14-20% efficiency. These cells must be
full encapsulated to prevent release of toxic selenium. These cells
have an open circuit voltage of 5 volts and a short circuit current of
95ma. Max power output is 3.9 volts at 64mA.
d. Organic photovoltaics (OPV)- currently maximum is 56.5 %. The Konarka Power Plastic is one of the few
commercially available OPV panel. The advantage of
organic or plastic solar cells is that they have the potential
of extremely low material and manufacturing cost and
they are flexible. A disadvantage is that organic materials
have a limited lifetime especially in full sun and exposed
to water and oxygen.
e. Dye Sensitized Solar Cell (DSS)Demonstrate the dye sensitized solar cell.
Follow the separate directions to activate a titanium dioxide coated ITO slide to
Photovoltaics Kit Page 2 of 19
form a Graetzel cell. Beginning with a pre-coated TiO2 / ITO slide, add berry juice
to sensitize the TiO2. Lightly coat the other slide with the carbon soot from a
candle. Pinch the slides together (carbon against TiO2) with the binder clips so
that the slides are offset exposing the conductive ITO layer. Apply iodide solution
as an electrolyte and then attach the alligator clips to the exposed edges of the
f.
Desktop Display – It’s convenient to mount the various demonstration cells on a
display board so that the leads hang free and can be connected in a variety of
ways. The output can be connected to a small motor with a rotating disc which is
safe and impressive to kids. For indoor demonstrations a 100 watt equivalent
fluorescent bulb (1700 lumens) in a clip on holder works well because it stays cool
and is safe around kids. Several of these can be used for more intensity or they
can be placed very close to the cells.
g.
Brainstorm what characteristics would be desirable for a solar cell. Some
possibilities power, costs, durability, flexibility, safety, ease of producing,
environmental safe and plentiful materials.
Research Connection: CMDITR Engineers and scientists are trying to develop the
next generation of solar cells using organic chemicals. The research connects
includes theoretical modeling of organic systems, synthesis, prototyping and testing.
Photovoltaics Kit Page 3 of 19
3) Series vs Parallel circuits
Several cells can be connected in series or parallel to get desired power
characteristics.
a. Explain the difference between voltage and current. Show that the large panel
produces a higher voltage (because it has several cell areas wired in series).
Measure the voltage and current produced from each cell using the digital
meter. The digital multimeter has a dial setting for measuring voltage and
amperage also note that the red lead must be moved and the selector switch set
to mA to get the ammeter mode. Each cell has a characteristic voltage. Silicon
cells produce between .5 -.6 V oc *(volts open circuit), OPVs are usually around
.4 Voc.
b. Explain the difference between series and parallel circuits. Use the clip leads
and the three small panels to demonstrate that in a series circuit the voltage is
added. In a parallel circuit the voltage does not change but the current
(amperage) is increased.
+ PV cell -
+ PV cell
+ PV cell -
+ voltmeter -
Series
+ PV cell Parallel
+ PV cell + PV cell + voltmeter -
c.
Research Connection: The voltage of photovoltaic cells are determined by the
bandgap of energy for the combination of chemicals or materials used. Even low
voltage devices can be combined in series or parallel circuits to get the correct power
for desired applications.
Photovoltaics Kit Page 4 of 19
4) Measuring Power
The power from a solar cell depends on the current and voltage. To measure the
power record the voltage and amperage of a solar cell across a load. The ammeter has
builtin precision resistors in its circuit. If you only had a voltmeter you could place a
known resistor in the circuit and calculate current in amps as voltage divided by ohms.
The peak power depends on specific load which affects the current and voltage. ( see
voltage current graph below) For this activity you measure the voltage and current in a
simple circuit without a load.
Solar Cell
A
V
P= V x I
Power (watts) = Volts x Amps
Sample calculation:
Volts = .4 V
Amp = 50ma= .05 amp
Power = .02 Watts
a. Compare the power for a 3 x 4 cm area for the crystalline solar cell compared to
the same area of amorphous silicon cell.
b. The amorphous panel provided is 7.2 V and 200 ma. How many of these
panels would be needed to in what configuration to generate 100 Watts?
c. Experiment with different sources of light, sunlight, or diffuse vs. direct light
d. Experiment with the effect of temperature on cell power.
Research Connection: CMDITR Engineers and scientists test their OPV cells in a
similar manner by measuring voltage and current under different loads and light
conditions to calculate the maximum efficiency. With a reliable way of comparing
cells then it is possible to fine-tune the systems and methods to improve efficiency
and longevity.
Photovoltaics Kit Page 5 of 19
5) Power : area relationship
The larger the cross sectional area of the light beam that is trapped, the greater
the power generated.
a. Cover portions of the panel to show decreasing current and voltage. Solar cells
measured with the meter are under no load so you get the open circuit voltage
(Voc). You should notice that the current responds quickly with decreasing light
while the voltage stays somewhat stable, finally the voltage drops too. To
measure the power from the panel you have to measure both voltage and
amperage produced.
b. Plot the power versus area for the amorphous silicon panel. Complete the table
and graph from BLM 1- Power vs Area Experiment
c. Repeat the measurement with a different
pattern of shading (block the left, right top or
bottom) You may get different results
because of the wiring of cells within the array.
Once a parallel section of panel is partially
shaded it tends to knock out the whole
section. Panels can also be equipped with
bypass diodes which reroute current around
underperforming cells.
http://www.electroiq.com/index/display/article
-display.articles.Photovoltaics-World.boscomponents.inverters.2009.03.shadehappens__installation.QP129867.dcmp=rss.
page=1.html
Research Connection: OPVs could be less expensive to manufacture so even if
they are less efficient a larger area could be deployed.
Photovoltaics Kit Page 6 of 19
BLM 1 Power versus Area Experiment
Purpose
Data Table
Area
Voltage
Current
Power
Power Watts
Data Analysis
Exposed Area (cm2)
Conclusions:
Photovoltaics Kit Page 7 of 19
6) Power : distance relationship
Energy from a radiant light source drops off with distance. As you move away from a
diffuse light source the same amount of light is spread over a large area so the solar
panel only intercepts part of the energy. This called the inverse square law. It relates I
intensity with r the distance.
If you use a focused light source up close this relationship will not hold. At the distance
we are from the sun it does not make any measurable difference how close (for example
sea level versus on mountain top) we place solar cells to the sun. There is some variation
in power available from the sun as we as the Earth’s orbit reaches perihelion. Currently
this occurs in January when the Earth is 5million km (3 million miles) closer to the sun.
This results in about 7% more solar energy striking the earth at perihelion.
Use the electric meter to measure the current produced by the sample silicon cell as you
move away from a light source. Collect data and graph the experiment using BLM 2 –
Power vs Distance Experiment
Research Connection: When testing solar cells identical conditions need to be
used. Typically a special “artificial sun” lamp with precise color balance and
uniform power is used to simulate natural sunlight. Distance from the source
must also be kept constant.
Photovoltaics Kit Page 8 of 19
BLM 2 Power versus Distance Experiment
Purpose
Data Table
Distance from Light
Source
Voltage
Current
Power Watts
Data Analysis
Exposed Area (cm2)
Conclusions:
Photovoltaics Kit Page 9 of 19
Power
7) Power : Incidence Angle relationship
The angle with respect to the sun influences the energy output. Changing the angle
has the effect of decreasing the cross section of light that is intercepted. You can see
this by measuring the shadow of the panel as it is
tilted. In addition low angle sun on the Earth must
pass through more atmosphere so some energy is
absorbed. This is described with the cosine law
which relates I the insolation to S the incident solar
energy (Watts/m2) and Z the Zenith angle of the
surface with respect to the sun.
I= S Cos Z
a. Set up the solar panel on its inclined
support with protractor. Change the angle of the solar panel and measure the
current. Plot the current versus the angle. Complete the data and graph on
BLM 3 Power vs Angle Experiment
b. Use this information to create a bar chart showing the total power generated by
a cell during the course of day if the cell were fixed on a roof with an angle of 30
degrees. The peak angle of the sun on the spring or autumn equinox is 90- your
latitude. At mid summer it is 90 – latitude -23.45 degrees. At mid winter it is 90
– latitude + 23.45 degrees
Research Connection: Engineers have designed tracking systems that keep PV
panels facing perpendicular to sun all day long. Others have explored using
concentrators or light guides to reflect light to a smaller area where the cell is.
Photovoltaics Kit Page 10 of 19
BLM 3 Power versus Angle Experiment
Purpose
Data Table
Angle
Voltage
Current
Power
Power Watts
Data Analysis
Angle with respect to light source- deg
Conclusions:
Photovoltaics Kit Page 11 of 19
8) Power vs Wavelength- Absorption
Photovoltaics absorb light at specific wavelengths. The sunlight that reaches the
Earth is spread over a larger spectrum. Some is visible and some stretches out into the
infrared and is invisible. The irradiance at the Earth’s surface shows distinct dips at
certain wavelengths due to absorption by atmospheric gases. Each kind of solar cell
absorbs efficiently distinct wavelengths. Characterizing the absorption spectra is
important.
a. Use the red, green and blue filters to show that certain colors when filtered out
reduce the power more than other colors. Refer to the transmission spectra
accompanying each filter to find its wavelength in nm.
b. Plot the current versus wavelength when different colors are placed in front of
the solar cell. You can use the large filter sheets or the filter sample booklets. Be
sure to pick filters with approximately the same optical density. Use the attached
transmission spectra tabs to pick colors that represent an even array across the
spectrum. Complete BLM 4 Power vs Wavelength Experiment
c. Compare the amorphous silicon, the polycrystalline silicon cell, and the dye
densitized solar cell.
Research Connection: When we design chemicals to use in organic photovoltaics
we measure the absorption spectra of the chromophores. Ideally we want dyes that
absorb across the entire visible spectrum.
Photovoltaics Kit Page 12 of 19
BLM 4 Power versus Wavelength Experiment
Purpose
Data Table
Wavelength Voltage
Current
Power Watts
Data Analysis
Wavelength nm
Conclusions:
Photovoltaics Kit Page 13 of 19
Power
9) Measuring Efficiency
Efficiency is a measure of how much of the available energy is captured by a cell. It
is the amount of electricity produced divided by the amount shining on the solar cell. To
measure efficiency we have to know how much light energy is hitting the cell and how
much electricity it is producing. It’s difficult to measure the incident light. Direct sunlight is
between 250 and 1,000 W/m2. .
a. In full sunlight measure the power of your solar cell and calculate the efficiency.
In this example the cell has an area of 2.4 x 10-3 m2 , measuring .6 Volts and .5
amps in full sun
Pi = A * Ps = 2.4 x 10-3 * 1000 = 2.4 watts
Po = V x I = 0.6 x 0.5 = 0.3 W
e = Po/Pi = 0.3/2.4 = 0.12 = 12%
b. Repeat this measurement for various cells. What difficulties do you notice in
comparing the efficiencies of various cells?
10) PV Cost estimation
Solar cells are still somewhat expensive. Several factors have to be considered in
sizing a solar system. Calculate how much area is needed to power a house, how much
would it cost?
a. Solar cells currently run about $5-$9 per peak watt.
b. A house might require 2kW peak power
c. If the silicon cells are 15% efficient and the
d. Incoming energy is 1000 W/m2 assume 5 hours (5 kWh/m2) per day of useful
sunlight or use the “Photovoltaics Solar Resource” map from NREL to identify
the available solar resource for your area.
e. If you aren’t connected to the grid you will need batteries which cost $1 amp
hour
Research Connection: Materials and manufacturing process determines the cost.
Organic photovoltaics have a potential of being low cost because they can be
manufactured with roll printing methods. Further research is needed to get higher
efficiency, better durability (through encapusulation and decreased photobleaching) New
organic solar cells may be much cheaper in the future.
Photovoltaics Kit Page 14 of 19
11) PV characterization
Solar cells are characterized using a voltage- current curve. Researchers build test
cells using different materials and techniques and then test them in a controlled way. A
common test is to create a voltage current plot. The curve goes between the open circuit
voltage (Voc) and the short circuit current Isc. If you measure the voltage of solar cell with
no load that is the open circuit. The maximum voltage occurs when there is no resistance
and no current. If you have an infinite resistance on the circuit there is no voltage but a
maximum current. Somewhere between these extremes is the peak power , a
combination of current times voltage which can be seen as the elbow on the voltage
current curve. In this experiment a variable resistor is used obtain a series of voltage
and current pairs.
a. Place the test PV cell in the wood test holder. Place an ammeter and a volt
meter at the two pegs labeled A and V. Gradually change the series load in the
circuit by sliding the variable resistor. Adjust the load to get an even series of
voltage readings such as every .1 volts and record the amps for each voltage.
Plot the data. The goal is to get a curve that is closer to a right angle (with a
minimum fill factor). There is a certain combination of voltage and current that
delivers peak power.
b. Complete BLM 5 Current vs voltage experiment
Research Connection: CMDITR researchers do this same measurement with much finer
control.
Photovoltaics Kit Page 15 of 19
BLM 5 Current voltage J/V graph Experiment
Purpose
Data Table
Voltage
(V)
Current(A) Power (A x
V)
Power mW
Current mA
Data Analysis
Voltage V
Conclusions: Jsc =______Voc= ______
Photovoltaics Kit Page 16 of 19
12) PV Characterization with Probeware
Researchers usually use computers to collect and analyze PV performance data. The Pasco
voltage/current probe connected to the USB link provides an easily visible display of solar cell
performance. To set up the experiment follow these directions:
1) Set up a solar cell at a set distance from a light source or in full sun. Be sure to keep illumination
constant through the measurements.
2) Connect the voltage probe to output of the solar cell using the black lead to the negative.
3) Connect the current probe to the output of the solar cell in series with a variable resistor. The
resistor will be used to decrease the current from Jsc where there is maximum current but no
voltage (since it is essentially a short circuit), to a maximum resistance Voc at which time there
is no current flowing through the resistor but maximum voltage. Variable resistors will have to
be carefully chosen 0-100, 0-500, 0-1000 are possibilities.
4) Open the DataStudio activity called JVcurve.ds. It will display a graph with amps on the y axis
and volts on the x, and a dial display for current and voltage meters. The sampling option is set
to “Manual Sampling” and “Keep data values only when commanded. On both meters and graph
the appropriate range is 0-.1 amps for current and 0-.5 volts.
Photovoltaics Kit Page 17 of 19
5) Click “Start” to begin viewing the current and voltage. The “Start” button turns to “Keep” with a
red stop square to the right. Each time you click “Keep” a data point is added to the graph at the
instantaneous current and voltage levels. This data set is known as a “run” and is noted in the
data summary area on the left with a matching icon on the graph. (An alternative method is to
set the sampling method to timed and then repeatedly change the potentiometer to fill in the
curve. Since this is continually collecting x,y points it can result in a large number of redundant
pairs but is more impressive as a dynamic display).
6) Adjust the variable resistor from 0 ohms to full resistance in series of steps. You’ll notice that as
the resistance increase the voltage increases and the current decreases.
Carefully adjust the variable resistor so that you get readings every .05 volts.
7) Click the red square to stop data collection. Click “start” to begin a new data set.
8) Repeat this measurement with different cell types, with different levels of illumination, and
using different color filters.
Links
http://www.nrel.gov/learning/re_photovoltaics.html
http://www.ccmr.cornell.edu/education/modules/documents/PhotovoltaicCells.pdf
http://www.infinitepower.org/pdf/No19%2096-828B.pdf
http://www.nrel.gov/midc/unlv/ live insolation data for Las Vegas
http://en.wikipedia.org/wiki/Solar_cell
http://www.powernaturally.org/Programs/SchoolPowerNaturally/InTheClassroom/kitlessons.asp
?i=9#Lesson14
Sources for kit materials
 http://shop.pitsco.com/store/detail.aspx?CategoryID=115&by=9&ID=2647&c=1&t=0&l=0
$8. 95 sunzoom lite car
 http://store.sundancesolar.com/subusobachki6.html 4 aa batter charger $39.95
 http://store.sundancesolar.com/misorokitsus.html mini solar car $9.95
 http://www.frys.com/product/5342528?site=sr:SEARCH:MAIN_RSLT_PG Electric Meter
$26.95
 http://scientificsonline.com/product.asp?pn=3039810 $5.95 each (3)
 http://scientificsonline.com/product.asp_Q_pn_E_3085037 $2.95 each CIS solar cell
 http://store.pasco.com/pascostore/showdetl.cfm?did=9&partnumber=PS-2100A&detail=1
Pasco PASPort USB link $59
 http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&PartNumber=PS2115&groupID=192&Detail=1 voltage/current probe $99
 http://k8.vernier.com/products/interfaces/ Vernier Go!Link USB interface (alternative to
Pasco version)
 Protractor
 Light Source for indoor use- quartz desk lamp
Photovoltaics Kit Page 18 of 19


Color Filter pack for testing cells
Rechargeable Batteries
Cost $55- 250
Photovoltaics Kit Page 19 of 19
Telecommunications and Lasers
Overview
One of the major research thrusts of CMDITR is organic electronics that can be used in
information technology and telecommunications. At the heart of this is the modulation of light
using new organic electro-optical materials. Students need to understand how the system
currently uses light and optics to carry information. Electro-optic materials can change their
index of refraction in the presence of an electric field. This property combined with wave
interference makes high speed switching possible. Finally, electro-optical and all optical
switches can be miniaturized to the nano-scale to take advantage of other unique properties in
device design.
Key Concepts and Demos
1) Analog vs Digital Signals
Information can be carried by modulating electrical signals either analog
(continuously changing) or digital (discrete values- coded in timed pulses either on or
off). Show or draw pictures of waveforms of analog and digital signals.
2) Light as a signal carrier
Information can be carried by light. Bounce a laser off of mirror attached to a balloon
stretched on a can. Tap the rubber membrane or speak into it. Brainstorm the
advantages of using light as carrier for information?
Research Connection: CMDITR is working on ways to modulate light by controlling
the optical properties of the materials it passes through. This may lead to improved
efficiency of switching light in communication systems. It also may lead to all-optical
switching (AOS) in which light from one channel controls light in another channel.
3) Fiber optics explanation
Optic fiber transmits light due to total internal reflection. Demonstrate light reflecting
inside of plastic hose filled with water. Fill the plastic chamber with water and add a
pinch of dry milk powder to reveal the light rays. Demonstrate the critical angle where
there is total internal reflection. Place a wood plug in the hole in the plastic bottle and fill
the bottle with water, place it on top of the plastic case. Position the laser in the support
so that it points directly at the end of the plug. Place the larger plastic tub below the
stream path. Turn on the laser and pull the plug. Use a white card to interrupt the stream
and demonstrate that light is internally reflected in the stream.
Telecommunications and Lasers Kit Page 1 of 6
The light fountain was first demonstrated by Daniel Colladon in 1842
Optical fibers have a variety of useful properties. Use the various materials in the
Adventures in Fiber Optics kit to demonstrate cladded and uncladded cables, floures
4) Index of refraction demo
Light is refracted and reflected when it encounters a material with a different index
of refraction. Place a straw in the plastic tub with water (add a little milk to visualize
laser) and observe that it appears to bend when placed at an angle. Repeat the
demonstration this time with a laser pointed down from above. Index of refraction is the
ratio of the speed of light in a vacuum over to that in the material. Air and water have
very different indexes of refraction.
5) Comparing index of refraction of substances
Various solids and liquids can have different indexes of refraction. Carefully pour a
layer of 80% sugar solution or corn syrup into the bottom of the plastic container. Tell
students that sugar water has index of refraction of 1.49 and pure water is 1.33. Repeat
the refraction demo. The light should bend a second time when it reaches the sugar
water layer. Another variation is to carefully mix a series of sugar solutions and layer
them so the solution is progressively more dense. This will result in a smoothly bending
straw or light beam.
Research Connection: This property is used in optic fiber in which the core and
cladding have different IOR. Some fibers use the graded index fiber with special
glass or polymers with progressively higher IOR. This decreases the dispersion of
light that is caused by light at different angles passing through the fiber at different
speeds (modal dispersion).
6) Optic Fiber Network Demo
Fiber optics are used to transmit signals over long distances for phone and
computer networks, or short distances between computer servers where high speed
connections are needed. This usually involves transferring from electrical to optical and
back to electrical signals. The optical fiber communications demonstration kit includes a
transmitter and a receiver. Apply the 5V power supply to the demonstration device. This
demo shows one way communication. (for two way communication the system would
have a receiver and transmitter at both ends). The transmitter has a simple oscillator that
controls an LED at the point where the optical fiber enters the device. Light passes along
Telecommunications and Lasers Kit Page 2 of 6
the fiber to the receiver where a photo detector senses the light and the circuitry coverts
the light back into electricity at the Data output lines. Connect EN and EXT on the
transmitter to the +5V positive terminal. An LED will flash on the Data lines on the
receiver, proving that the signal has made it all the way back to electricity again.
Disconnect the optical fiber from the receiver end and show that that the fiber end is
flashing, the LED on the data will stop flashing when it stops getting its optical signal. As
you bring the fiber back into the receiver the LED will begin flashing again.
The circuit is controlled with the following logic on the transmitter side. 0 means the line
is connected to the ground, 1 means it is connected to the +5V line.
Mode EN
1
0
2
0
3
1
4
1
EXT
1
0
1
0
LED State
ON
OFF
OSCILLATING
OFF
Research Connection:CMDITR researchers are concerned with various aspects of
the optical network. An electro-optical switch can built using polymers. A key problem
is switching speed. New organic molecules may be able to operate at higher speeds
than current materials.
Telecommunications and Lasers Kit Page 3 of 6
7) Polarizing Filter with Laser
Telecommunications depend on the ability to turn light on and off quickly
(modulation). Show how the polarizing filter can pass or block light from the laser
pointer.
8) Michelson Interferometer
Coherent light can be modulated by using interference of light waves. The MachZehnder (MZ) interferometer is a device used to modulate light. In the MZ device a light
beam is divided into two paths and one path goes through some electro-optic material.
Changing the electric field on the EO material changes its index of refraction. When the
two paths converge again destructive interference cancel the output light creating a
signal.
A Mach-Zehnder device
The Michelson Interferometer demonstrates this kind of interference with a more
complicated path. One path of the split beam goes through the beam splitter, reflects off
a mirror, then reflects off the back side of the image splitter and finally reflect off a
second mirror before exiting the beam splitter along the original path. The two beams
then pass through a diverging lens to spread the beam out into a wider area to reveal a
series of bands or circles where there has been interference. This device is extremely
sensitive to distance (for visible light it is 1/100th the thickness of human hair. This makes
it sensitive to minute vibrations and minute changes in the index of refraction of material
placed in the path.
The Michelson Interferometer Light Path
Follow the manufacturer’s instructions for arranging the pieces for the interferometer
demo. Once you get a somewhat stable interference pattern then experiment with
placing glass in the path. By turning the glass slightly you will alter its effective index of
Telecommunications and Lasers Kit Page 4 of 6
refraction and cause a shift in the interference pattern. Similarly, when an electro-optical
material is placed in the beam path it will alter the interference pattern. A variation on
this setup can be used to measure the electro-optic coefficient of materials.
Research Connection: CMDITR research is building materials that can be used in
telecom and all optical switching.
9) New materials can be fashioned into extremely small nano-scale devices integrated right
on to the chip. Show photos, discuss micro-electronic trends, fabrication and scale.
Sources for Materials
 http://www.i-fiberoptics.com/laser-kits-projects-detail.php?id=2110 Michelson
interferometer with pointer $109
 http://www.i-fiberoptics.com/educational-detail.php?id=14200 Educational
Communication Kit $18 includes fiber, LED photodetector
 http://i-fiberoptics.com/educational-detail.php?id=13700&cat=kits-projects Adventures in
Fiber Optics Kit $42
 Laser pointer $14
 plastic tray, pop bottle, milk.
 Nanophotonics pictures
 Plastic tube with clear plastic ends
 Radioshack dpdt submini switch- 275-0407 $3
 5V DC power supply-
Cost $141- $300
Telecommunications and Lasers Kit Page 5 of 6
Links
http://en.wikipedia.org/wiki/Interferometer
http://depts.washington.edu/cmditr/mediawiki/index.php?title=Dispersion_and_Attenuation_Phe
nomena
http://depts.washington.edu/cmditr/mediawiki/index.php?title=Optical_Networks
Telecommunications and Lasers Kit Page 6 of 6