Download SolarEnergy_Kit#1 - Institute for School Partnership

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Contents:
Investigating Light Quality and Absorption of Light by Plants
Topic Template
Background
Model 1: Electromagnetic Radiation
Model 2: Energy Content of Light
Model 3: Sunlight Reaching the Earth
Model 4: Measuring Light
Kit #1 LAB: Investigating Light Quality
Kit #1 – Add-on A Lab: Chlorophyll Spectroscopy & Fluorescence
Kit #1 – Add-on B Efficiency of Photosynthesis
Photos of Kit Components
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Topic Template
Topic
Associated Curriculum
Associated Content
Investigating Light Quality and Absorption of Light by Plants
Solar Energy
Plant Science, Photosynthesis, Electromagnetic Radiation, Energy
Materials Needed
SpectroVis Plus
Fiber optic cable
LabQuest
Discuss how a lamp, a microwave, a television, and a radio all
related.
• What other things in the world move in waves?
• How do we use instruments that transmit and detect light to extend
our senses?
• Discover which wavelengths of light are used by plants for
photosynthesis.
• Design a model for how energy moves from the sun to plants to
humans.
MSPS4-1 Use mathematical representations to describe a simple model for
waves that includes how the amplitude of a wave is related to the energy in
a wave.
MSPS4-2 Develop and use a model to describe that waves are reflected,
absorbed, or transmitted through various materials.
MSLS1-6 Construct a scientific explanation based on evidence for the role of
photosynthesis in the cycling of matter and flow of energy into and out of
organisms.
Sunlight reaches earth in the form of waves. Certain waves are utilized by
plants to undergo photosynthesis. This energy is the foundation of almost all
life on earth.
Model of Wave NEEDS TO BE CREATED*** (Sunlight travels from the sun to
earth in waves. These waves have specific parts which are measurable.)
Electromagnetic Radiation (Electromagnetic waves are measured in
frequency or wavelength and have many different properties based on these
values.)
Energy Content of Light (EM waves transmit energy and that energy
increases with an increase in frequency or a decrease in wavelength.)
5E Learning Cycle
• Engagement
• Exploration
• Explanation
• Elaboration
• Evaluation
Related NGSS
Standards
Background/Why
Model 1 (Essential)
Model 2 (Essential)
Model 3 (Essential)
•
•
•
•
Model 4
(Essential/Extension)
Sunlight Reaching the Earth (The sun is millions of miles away yet it takes
only minutes for the EM waves of the sun to hit the earth. Also, the amount
of energy that hits the sun can be calculated by finding the solar constant)
Model 5 (Extension)
Measuring Light (Light can be measured in many different ways depending
on what you want to find out)
Lab (Extension)
Investigating Light Quality (Not all light is the same, and it can be measured
using scientific instruments for different properties. Plants use specific
wavelengths of light.)
3 Investigating Light Quality and Absorption of Light by Plants
The Big Idea:
Core Idea in the Framework for Science Education (NRC, Draft, July 2010)
PS 4: Our understanding of wave properties, together with appropriate instrumentation, allows
us to use waves, particularly electromagnetic waves, to investigate nature on all scales, beyond
our direct sense perception.
LS 1: Organisms have structures and functions that facilitate life processes.
WHY?
Sunlight is the total wavelength (or frequency) spectrum of electromagnetic radiation given off
by the sun. Sunlight consists of all the colors of the visible spectrum as well as UV-rays and
radiant heat. On Earth, sunlight is filtered through the Earth’s atmosphere and experienced as
sunshine. Sunlight is a key factor in photosynthesis, a process vital for life on Earth. We can use
optics to display the relative intensities of the various wavelengths of light that are emitted from
sun. Determining the quality of light is especially important because we know that the process
of photosynthesis is more efficient at certain wavelengths (colors of light). Because
photosynthesis on land and in oceans produces eight times the present combined energy
requirements of humanity, maximizing its efficiency as a renewable energy source is essential.
At this time, we use a significant fraction of this energy but we could learn to use it even more
effectively in the future.
Background:
The process of photosynthesis involves the use of light energy to convert carbon dioxide and
water into sugar, oxygen and other organic compounds. It is the light reactions of
photosynthesis that require this light energy to excite the chlorophyll (or bacteriochlorophyll)
molecules and cause electrons to move through the electron-transport chain.
Light has the mysterious property that it can be described both as an electromagnetic wave or
as a particle. The wavelength is measured in nanometers (nm), which is 10-9 meters. An
individual particle (unit or quantum) of light is called a photon. Since individual photons
possess tiny amounts of energy, it takes many many to obtain a measurable amount of energy.
Counting photons is done in units of moles (mol), for which there are 6.02 x 1023 photons/mol.
Photons have different amounts of energy, determined by their wavelengths (colors). Light
quality is the relative number of light particles at each wavelength. Light quality refers to the
spectral distribution of light, or the relative number of photons of each portion of the light
spectrum (visible and invisible) emitted from a light source, including the sun.
Light has an economic value. As the driving force for photosynthesis, light is fundamentally
important to crop production. Plant growth and development is significantly influenced by both
the quantity and quality of light. Measuring light accurately requires the proper (correct) meters
and methods.
4 A pyrheliometer is a broadband instrument for direct measurement of solar irradiance. Sunlight
enters the instrument and is directed to a thermopile, which converts heat to an electrical signal
that can be recorded. The instrument is always aimed directly at the sun, often via a tracking
mechanism that continuously follows the sun. It is sensitive to wavelengths in the band from
280 to 3000 nm. Typically, these measurements are made for scientific meteorological and
climate observations, material testing research, assessment of the efficiency of solar collectors,
and for setting up photovoltaic devices. Foot-candle meters measure illuminance or light
intensity using the unit of a foot-candle. Foot-candle meters measure light similar to how the
human eye perceives brightness: strongest in the 500-600 nm range. Since light intensity is an
important factor in the photosynthesis of plants, horticulturalists often measure and discuss
optimum intensity for various plants in foot-candles. However, photosynthesis is also impacted
by the wavelength of light reaching the photosynthetic organism. To measure the quality of
light a specific type of spectrophotometer is used. Spectroradiometers are calibrated
spectrometers with the correct geometry to characterize light sources. Typically, models cost
about $5000.00 and are calibrated to measure absolute spectral irradiance of light sources.
However, using the optical fiber attachment of the SpectroVis Plus, we can measure relative
spectral irradiance of light sources. The spectroradiometer can be used for solar studies and
other photochemistry applications.
5 MODEL 1: Electromagnetic Radiation
What is the range of frequencies that constitutes visible light? What is the range of
wavelengths?
Arrange the types of electromagnetic radiation in order from shortest wavelength to longest
wavelength. Be sure to split visible light into its constituent colors.
What type of electromagnetic radiation has the highest energy? What type has the lowest
energy?
Use the equation c = wavelength x frequency, where c is the speed of light. From the data for
infrared radiation, calculate the speed of light. How does it compare with the standard?
6 MODEL 2: Energy Content of Light
What is the energy in Joules of a typical infrared photon?
What is the energy in Joules for a typical ultraviolet photon?
Do the numbers you calculated make sense according to your knowledge about the energy of
electromagnetic radiation?
Exercises:
Rank the following photons in order of increasing energy: UV, microwave, x-ray, visible,
radiowave, IR, gamma ray.
Complete the following table:
7 MODEL 3: Sunlight reaching the Earth
Calculate the time it takes a photon of light emitted by the sun to reach Earth.
Bodies of the solar system such as planets receive light at an intensity inversely proportional to
the square of their distance from the sun. What is the intensity of light that reaches Earth from
the sun?
Calculate the solar constant using the following information and Model 3:
So = E(Sun) x (R(Sun) / r)2
So = Solar Constant
E= Surface Irradiance of the Sun
R= 6.96 x 105 km = Radius of the Sun
r = Average Sun-Earth Distance
Based on this information, how would you define the solar constant?
The solar constant is defined as the quantity of solar energy at normal incidence outside the
atmosphere at the mean sun-earth distance. The approximate value of the solar constant is
equivalent to 1.96 calories per minute per square centimeter, or 1.96 langleys (Ly) per minute
8 MODEL 4: Measuring Light
Background:
Radiometry versus Photometry
Radiometry is the measurement of electromagnetic radiation in the ultraviolet, visible and
infrared regions. It is typically measured in watts/m2. Photometry is limited to the visible
spectrum as defined by the response of the human eye (360-830 nm). Typical units include
lumens, lux, candelas, etc.
Pyrheliometer
This instrument is designed to measure the direct solar
irradiance. The detector at the bottom of the collimator tube
is a black painted brass cylinder to which a digital
thermometer probe has been mounted. Only the direct rays
of the sun (and some circumsolar - surrounding the sun radiation) reaches the detector. Using the pyrheliometer
equation, you can calculate the solar irradiance from the
heating of the brass cylinder. Measurements throughout the
day permit the solar constant to be determined. The
technique was first used by Pouillet in France in the 1830's
and later by John Ericsson in the USA who was able to
determine the solar constant with
remarkable accuracy.
Foot-Candle Meter
Units:
• Candela (cd): fundamental unit of all photometry that corresponds to
the amount of light--quantity of photons--produced by a standard light
source. Originally, the standard source was a real candle. Today, it's a
theoretical construct, like most measurement standards.
• Lumen (lm): unit of luminous flux, or amount of light radiating out
from a light source through a specific solid angle or cone of space.
The efficiency of light sources is assessed by comparing the energy
input in watts with the luminous output in lumens (lm/W).
• Foot-Candle (fc): a hybrid unit, which uses a metric measurement for luminous flux, in
combination with the square-foot for the unit of area. There are about 10.76 square feet
to the square meter. The foot-candle meter is an instrument for measuring light levels in
terms of foot-candles.
How many lux is one foot-candle?
Using date from the table above calculate the
luminous flux in lux recommended for reading
or studying.
9 Spectroradiometer/Spectrophotometer/Spectrofluorometer
In the SpectroVis Plus, when used as a spectrophotometer, light
from the LED and tungsten bulb light source passes through a
solution. Emerging light goes through a high-quality diffraction
grating then the diffracted light is collected and sorted by the CCD
array detector. (A diffraction grating works like a familiar prism and
sends the different colors of light in slightly different directions, as
shown in the figure.)
For fluorescence (on type of light emitted by a molecule or
body), SpectroVis Plus has two different excitation
wavelengths to elicit the fluorescence emission, so now you
can quantitatively measure the fluorescence spectra of many
compounds, such as quinine, fluorescein, and chlorophyll.
For emission-intensity measurements, SpectroVis Plus uses
an optical fiber attachment. The optical fiber collects light to
the detector which transmits the measurements to the computer or LabQuest.
Classify the instruments into two columns, one which represents instruments used in
photometry and one representing instruments used for radiometry.
What other questions do you still have about measurements related to the quantity and quality
of light?
10 Lab Protocol: Investigating Light Quality
At this station, you will have the opportunity to use the Vernier SpectroVis Plus with an optical
fiber to visualize electromagnetic waves.
NGSS CONNECTIONS:
Kindergarten.
K. Weather and Climate
K-PS3-1: Make observations to determine the effect of sunlight on Earth’s surface
Grade 1.
1. Waves: Light and Sound
1-PS4-3: Plan and conduct an investigation to determine the effect of placing objects made with
different materials in the path of a beam of light
Grade 4.
4. Energy
4-PS3-2: Make observations to provide evidence that energy can be transferred from place to
place by sound, light, heat, and electric currents
Grade 5
5. Matter and Energy in Organisms and Ecosystems
5-LS2-1: Develop a model to describe the movement of matter among plants, animals,
decomposers, and the environment
Middle School
MS. Waves and Electromagnetic Radiation
MS-PS4-2: Develop and use a model to describe that waves are reflected, absorbed, or
transmitted through various materials
MS. Matter and Energy in Organisms and Ecosystems
MS-LS1-6: Construct a scientific explanation based on evidence for the role of photosynthesis in
the cycling of matter and flow of energy into and out of organisms
Background Information:
The electromagnetic spectrum is the
range of all types of electromagnetic
radiation. Radiation is energy that
travels and spreads out as it goes –
the visible light that comes from a
lamp in your house and the radio
waves that come from a radio station
are two types of electromagnetic
radiation. The other types of radiation
that make up the electromagnetic
spectrum are microwaves, infrared
light, ultraviolet light, X-rays and
gamma-rays.
11 Spectroscopy is the study of the interaction between matter and radiated energy. Spectroscopy
originated through the study of visible light dispersed according to its wavelength, e.g., by a
prism. Spectroscopy was expanded to include other forms of electromagnetic radiation.
Spectroscopic data is often represented by a spectrum, a plot of the data as a function of
wavelength or frequency.
INVESTIGATION:
You will use a type of spectroscopy to investigate the quality of different light sources, explore
the ways in which light energy is transmitted and absorbed by different objects (including a
plant) and draw conclusions about energy efficiency of light sources based on the type of
electromagnetic radiation represented by a spectrum.
ENGAGE
What is white light?
Use a prism to see this! Darken the room as much as possible to be able to see the full
spectrum of dispersed light.
Do you think all light has the same components?
Diagram:
ENGAGE
The instrument you will use today is called a SpectroVis Plus.
This instrument is able to not only separate light, but to also
measure the amount of light of each color (wavelength and
frequency) that is produced by a particular light source.
Brainstorm the different light sources and places where light
shines.
Some possible ideas include:
a. Fluorescent light bulb
b. Incandescent light bulb
c. Full spectrum light bulb
d. LED light bulb
12 e.
f.
g.
h.
i.
j.
k.
l.
Heat bulb
Laser
Full sun
In the shade of a building
Under a tree
Under a green leaf
Under a flower
Under different color leaves
EXPLORE
Choose various light sources that to test and compare.
In order to complete this investigation, here is a detailed procedure for how to use the
SpectroVis Plus:
1. Use the USB cable to connect the SpectroVis Plus to LabQuest
2. Turn on LabQuest. The default setting is absorbance, but we want to measure intensity
3. Insert the SpectroVis optical fiber into the SpectroVis Plus cuvette holder, lining up the
white triangles
4. On the LabQuest, choose Change Units ! USB: Spectrometer ! Intensity from the
Sensors menu. SpectroVis Plus measures intensity in relative units scaled from 0 to 1
5. Aim the tip of the optical fiber cable towards the sun to gain a reading for a solar
spectrum in full sun.
6. Record your location.
7. Start data collection to generate a spectrum.
8. Tap the red Stop button to stop.
a. Note: If the spectrum maxes out, increase the distance between the light source
and tip of the optical fiber cable by tilting the optical fiber OR reduce the Sample
Time and/or reduce the Samples to Average in the data collection dialog. To do
this, return to the Meter tab and choose Data Collection from the Sensors menu.
9. Click the File Cabinet icon, next to Run 1. This will create Run 2 for you to generate a
new spectrum.
*Be sure to keep track of Run 1, Run 2, etc. for data analysis later!
10. Choose another location and point the optical fiber cable upward.
11. Start data collection to generate a spectrum
12. Tap the red Stop button to stop.
13. Choose 4 more locations across campus and repeat Steps 10-13.
14. Save your file by selecting the File menu then Save. Name and save your file.
15. Turn off the LabQuest and meet back in the lab for analysis.
16. Transfer the data to the computer. This can be done in 2 ways:
a. Transfer data to a thumb drive
1. Plug thumb drive into USB port
2. Follow directions on screen to save data to thumb drive.
b. Transfer data directly to the computer
1. Open LoggerPro on your computer
2. Connect the LabQuest to the computer using the USB cable
3. The most current data will be retrieved automatically
13 4. IF NOT, in LoggerPro, go to File ! LabQuest Browser ! Open to open the
file from the LabQuest in LoggerPro.
5. If you data does not show up on the graph, go to Options ! Graph Options
! Axes Options and look where it says Y-Axis. Be sure there is check the box
of each run you would like to see on the graph
17. Change the names of runs to describe the data. Double click on the data set “Run 1”
and type in a descriptive name for this run.
18. Repeat Step 17 for the rest of the runs.
Changing the Settings for the SpectroVis Plus in LabQuest
The Spectrometer settings screen lists all of the settings for the device. To display this screen,
navigate to the Meter screen and choose Data Collection from the Sensors menu. Here, you can
adjust four parameters:
• Sample Time: similar to the shutter speed of a camera. For studies of intensity, you may
want to reduce the sample time as there is no calibration available for this setting.
• Wavelength Smoothing: the number of adjacent readings on either side of a given value
that is used to calculate an average value.
• Samples to Average: the number of readings taken at a given wavelength to calculate
an average reading.
• Wavelength Range: the range is determined by the type of spectrometer in use, but can
be changed to select a narrower range.
EXPLAIN
Fluorescent Light vs. Incandescent Light vs. LED
The impending ban on incandescent light bulbs has found many vocal opponents, including
those who say compact fluorescent bulbs just can’t match the warm glow of old-fashioned
incandescent.
Based on the data you collected are the opponents right?
Spectrum collected from an old-fashioned incandescent light bulb, a full spectrum incandescent
light bulb and a fluorescent light bulb using the SpectroVis Plus with optical fiber
14 Here’s another representation of the irradiance of four different light sources:
From: www.popularmechanics.com
An incandescent light bulb emits light by heating a tungsten filament surrounded by various
inert gases to about 4000 F. These lights release 90 percent of their energy as heat.
Does your data show that incandescent light bulbs emit energy as heat? Explain.
Inside a compact fluorescent lamp (CFL) an electric current is driven through a tube filled with
argon and a small amount of mercury vapor. This creates invisible UV light which excites a
phosphor coating that reacts by emitting visible light.
Use your data to explain why people don’t like they way light from CFLs looks.
Use your data to explain why CFLs are more efficient than incandescent light bulbs.
Light-emitting-diodelamps (LEDs) are composed of two conjoined sections of a semiconductor
material. When an LED is energized, movement of electrons across the diode causes emission
of photons – or light.
Based on the data, is the quality of the LED most similar to incandescent light or fluorescent
light?
15 Under a Leaf
You can measure the spectrum of light underneath a leaf to be able to see how electromagnetic
energy flows into and out of a plant. This investigation also gives you data that allows you to
draw conclusions about why when we look at a plant, it looks green.
A.
B.
The figures above show the comparison of spectra of sun’s radiation at different locations. (A)
Relative intensity of solar radiation. (B) Relative intensity of solar radiation beneath a tree.
Spectrum B highlights the maximum absorption of blue light and red light by chlorophyll of a
plant. This shows how a plant absorbs energy and explains why we see a plant as green.
The red edge can also be observed at wavelengths beyond 700 nm. Red edge refers to the
region of rapid change in reflectance of vegetation in the near infrared range of the
electromagnetic spectrum. Chlorophyll is responsible for this red edge, which is used to monitor
plant activity. IT has been suggested that the red edge could be useful to detect lightharvesting organisms on distant planets using spectroscopy.
Based on your data, what type of light would be best suited for plants?
Other Observations to Explain
What else did you notice?
What questions do you still have?
Draw Conclusions
What did you learn from this investigation? What did your data tell you about the different light
sources you observed?
16 ELABORATE (Kit #1 Add-ons A and B)
Consider and explain what you would change if they could do the investigation again.
What are other questions that you have generated by doing this investigation?
Add-on A: Chlorophyll Spectroscopy & Fluorescence
One possible investigation you might consider would be connecting what you have learned
about the quality of light and how electromagnetic radiation flows into and out of a plant, to the
absorbance of the pigment chlorophyll in plants and photosynthetic bacteria.
Lab Protocol: Chlorophyll Spectroscopy
Purpose: To measure the absorbance of chlorophyll a and b.
Materials:
• Fresh spinach
• Fresh carrots
• Mortar and pestle
• Grater
• 70% Isopropanol
• Acetone or petroleum ether
• Vernier SpectroVis Plus
Procedure:
1. Measure out 0.5 g of fresh spinach. Tear the spinach into tiny pieces and grind them
with a mortar and pestle. Add 20 mL of 70% isopropanol (IPA) and transfer the mixture
to a small beaker. Allow the mixture to sit.
2. Measure out 0.5 g of carrot slices (or shavings) and place them in a container. Add 20
mL of either acetone or petroleum ether to the flask and stopper it.
3. Calibrate the SpectroVis Plus using the solvent used in your sample
4. Place prepared spinach sample in cuvette
5. Record absorbance
6. Repeat step with carrot sample
Sample
17 Lab Protocol: Chlorophyll Fluorescence Lab
Purpose: To extract chlorophyll from leaves and show that it absorbs light and emits the
energy absorbed at a different wavelength, a phenomena known as fluorescence.
Background: Plants and algae have utilized chlorophyll molecules for millions of years to
harness the energy of the sun in order to grow and reproduce. Normally this energy is
absorbed and then used to undergo photosynthesis, the process by which plants create food.
However, by extracting the chlorophyll from leaves and suspending it in acetone or alcohol,
light energy is instead emitted in the red spectrum via fluorescence, as well as producing heat.
Materials:
•
A Handful of spinach leaves or similar dark green leaves (the darker the green the
greater the amount of chlorophyll)
10 – 15 mL Acetone or denatured alcohol
Filter Paper (Coffee filters work but are very time consuming)
Funnel
Test tube
Mortar and Pestle (or small blender)
Black Light and Dark room (could use a dark box with an eye hole)
•
•
•
•
•
•
•
Procedure:
1. Grind the leaves in the mortar and pestle (this works far better if leaves are freeze-dried
or frozen)
2. Add 10-15 mL Acetone or alcohol to the mortar and mix.
3. Fold filter paper and place in funnel and place funnel on test tube
4. Pour mixture from mortar through filter, being careful not to overflow.
5. Once it is all filtered, take test tube to the dark room and shine the black light on it.
Record your results.
Extension:
•
•
This reaction also produces measurable heat. Record temperature of test tube before
and after 5 minutes in the black light. Make sure heat is not transferred by hands.
If denatured alcohol is used, the fluorescence can be measured using a Vernier SpectroVis Plus. Set the excitation to 575 nm. Record the emission.
Going Further:
•
Draw a model of the experiment showing the black light, the chlorophyll in the tube, and
what is emitted.
18 Add-on B: Efficiency of Photosynthesis
One possible investigation you might consider would be connecting what you have learned
about the quality of light to the rate of photosynthesis. Dissolved oxygen sensors are an
available material that might be useful as you think about designing this investigation.
How could the dissolved oxygen sensor and the SpectroVis Plus with optical fiber be used to
connect the quality of light to the process of photosynthesis?
19 20