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See the Light by Making a Cell Phone Spectrophotometer

Difficulty
Time Required Long (2-4 weeks)
Prerequisites None
Material Availability You will need to special-order some items. See the Materials and Equipment list for details. A cell phone with a functional camera is required. A computer that can run Windows® software is required.
Cost Average ($50 - $100)
Safety No issues

Abstract

We encounter an amazing array of colors every day, from the greens of plants and the many colors of their flowers, to the pinkish blue of a sunset, to the artificial coloring in beverages. How do we perceive all of these colors? When light hits an object, some of that light is absorbed by the object, and the light that is not absorbed is what we see. In this science project, you will build a simple spectrophotometer from a cell phone and use it to investigate how visible light is absorbed by differently colored solutions.

Objective

Build a spectrophotometer and use it to investigate the absorption of visible light in differently colored solutions.

Credits

The design for the cell phone spectrophotometer was based on:

Teisha Rowland, PhD, Science Buddies
Andrew Bonham, PhD, Metropolitan State University of Denver

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Last edit date: 2012-12-07

Introduction

In biology and chemistry laboratories, researchers often use an expensive instrument called a spectrophotometer, which measures the intensity of light. Although this instrument usually costs hundreds to thousands of dollars, using a cell phone camera and less than $60 in other parts, you can build a rudimentary version of this really useful piece of equipment. Spectrophotometers have a wide variety of applications; they enable researchers to investigate topics such as how chemicals react, how quickly microorganisms multiply, and how much protein or DNA is present in a sample. To understand how a spectrophotometer can do all of these things and more, it is important to step back and learn about the basic concepts underlying how a spectrophotometer functions.

Visible light, the light that we can see, is electromagnetic radiation that the human eye can detect. Electromagnetic radiation is energy in the form of electric and magnetic fields that move through space as waves, and it manifests not only as visible light, but also as x-rays, radio waves, microwaves, and more. Watch this video to learn more about electromagnetic radiation.

Light and electromagnetic radiation video.
Watch this video
which gives an introduction to light and electromagnetic radiation.

Different forms of electromagnetic radiation, such as x-rays and visible light, have different wavelengths, as shown in Figure 1 below, but they all travel at the same speed - the speed of light. A wavelength is the distance between a point on a wave and the same point on the next wave, or, in other words, the distance that the wave travels in one cycle. Very short wavelengths, such as the ones that make up visible light, are measured in nanometers (nm) (1 nm = 1x10-9 meters).

The electromagnetic spectrum showing the visible wavelengths.
Chemistry science project
Figure 1. The electromagnetic spectrum and the wavelengths of visible light. X-rays, visible light, and radio waves are examples of electromagnetic waves. Visible light is the part of the electromagnetic spectrum that we can detect with our eyes. At the blue end of the visible spectrum, the wavelength of light is shorter (about 400 nm). At the red end of the spectrum, the wavelength is longer (about 700 nm).

For humans, the range of visible wavelengths is from 400 nm to 700 nm. We can see electromagnetic radiation in the visible light range because there are molecules in our eyes (called rhodopsins) that respond to different light wavelengths, and our brain interprets their responses as different colors. (The energy of the different wavelengths actually causes rhodopsin to change its structure.)

White light contains all of the visible wavelengths. When shone through a colored solution, the solution absorbs some wavelengths of the white light and transmits wavelengths that are not absorbed. When we look at the colored solution, we see the transmitted light. The transmitted light may be the only wavelength that is not absorbed. For example, if a solution absorbs all wavelengths except blue, the transmitted light will be blue. Similarly, the transmitted light can be complementary to the only absorbed color. Complementary colors are based on the three primary colors (red, yellow, and blue) and the secondary colors that are made by mixing two of these primary colors (orange, green, and violet). When two primary colors, for example, yellow and red, are mixed together, they create a secondary color, in this example orange, that is complementary to the third primary color, blue in this example. This is why if only orange light is absorbed from a solution, leaving primarily blue light to be transmitted, we see the solution as blue. Similarly, a solution may appear blue if it absorbs both red and yellow light. On the artist's color wheel in Figure 2 below, complementary colors appear on the opposite sides of each other.

An artist's color wheel showing the primary colors, secondary colors, and wavelength ranges of these colors.
Chemistry science project
Figure 2. This artist's color wheel shows the primary colors (red, blue, and yellow) and the secondary colors that are made by mixing two of these primary colors (orange, green, and violet). Approximate wavelength ranges for these colors are given in nanometers (nm). A color's complementary color is on the opposite side of the wheel. (Based on a figure from Martin Silberberg's Chemistry: The Molecular Nature of Matter and Change; McGraw-Hill, 2011.)

A spectrophotometer measures the intensity of light at different wavelengths by separating white light into a spectrum of colors, like a rainbow, when it passes through a colored solution. The amount of light that is transmitted is measured by a light detector on the exit side of the solution, or sample. Consequently, the spectrophotometer can create an absorption spectra for the sample, as shown in Figure 3 below, which shows which wavelengths are being absorbed the most by the sample.

Absorption spectra of blue #1 and red #40, showing their absorption peaks.
Chemistry science project
Figure 3. Absorption spectra of the food dyes blue #1 and red #40. Note that the blue dye absorbs light strongly at a wavelength of about 620 nm, which is in the orange part of the visible spectrum (see Figure 1 for colors and wavelengths). The red dye #40 absorbs strongly at around 500 nm, roughly in the blue-green part of the spectrum. The molar extinction coefficient, also known as the molar absorption coefficient, is a measure of how efficiently the light is absorbed at a given wavelength. (Thomasson, 1998.)

In this science fair project, you will build a simple spectrophotometer to measure the absorption of visible light in differently colored solutions. You will place the sample solutions next to a light source, then put a diffraction grating between the samples and the detector. You will make the sample solutions using water and different food colors, and the light source will be a white light-emitting diode (or LED). Diffraction gratings are used in spectrophotometers to split and diffract beams of light in different directions, or, in other words, to essentially create a rainbow of colors, which is used to analyze the samples. The detector will be a cell phone camera, which you will use to collect images. You will analyze your images using a computer software program that measures the amount of light that was transmitted through the sample. Much of this experiment will focus on optimizing, or improving, your spectrophotometer, to make it work the best it can given its inherent limitations.

Terms and Concepts

  • Spectrophotometer
  • Visible light
  • Electromagnetic radiation
  • Wavelength
  • Electromagnetic spectrum
  • White light
  • Absorption
  • Transmission
  • Complementary colors
  • Primary colors
  • Secondary colors
  • Spectrum
  • Absorption spectra
  • Molar extinction coefficient
  • Light-emitting diode (LED)
  • Diffraction grating
  • Maximum absorbance
  • Beer-Lambert law

Questions

  • What is an absorption spectrum?
  • What color is complementary to yellow?
  • What wavelengths do you expect a solution with yellow food color to absorb or transmit?
  • If the absorption spectrum for a solution with yellow food color had two peaks, what might you expect the wavelengths of the two peaks to be?

Bibliography

These resources are a good place to start gathering information about electromagnetic radiation, visible light, and spectrophotometers:

Information about the maximum absorbance of FD&C dyes in Table 1 was taken from this source:

Materials and Equipment

  • A hard, flat surface in a room that can be made very dark, or a piece of wood at least 40 cm by 15 cm that can be taken into a room that can be made very dark
  • Metric ruler or measuring tape
  • A small, visible-light diffraction grating; a 500 lines/mm (12,700 lines/inch) linear grating is recommended, such as the Diffraction Gratings Slide - Linear 500 line/mm sold by Amazon.com.
  • Transparent adhesive tape
  • A small, white LED bulb. Specifically a 5 mm white LED (part # RL5-W5020) is recommended, which can be purchased at superbrightleds.com
  • Battery, CR2032, 3V 20 mm coin. The battery can be purchased at Digi-Key.com or electronics stores.
  • Electrical tape
  • A small piece of wood or polystyrene, about 2 cm thick, or a baseplate template, large enough to place the light source on top of
  • Cups (one for each food color you want to test)
  • Water
  • Graduated cylinder, 10 mL, which can be purchased at Amazon.com, or measuring spoons
  • Food colors, including blue, red, and yellow
  • Cuvette, 3.5 mL (at least 4). Plastic cuvettes can be purchased at Amazon.com or Vernier.com
  • Optional: Medicine dropper
  • Cell phone with camera
  • Pencil
  • A computer that can run Windows® software
  • Lab notebook

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Experimental Procedure

Assembling the Spectrophotometer

In this part of the science project, you will assemble the cell phone spectrophotometer. You will need a hard, flat surface that can be used in a dark room, and on this surface you will position your diffraction grating and light source (the LED bulb) in such a way that you can see a line of colors, or spectrum, coming through the center of the diffraction grating.

  1. You will be assembling your spectrophotometer on a hard, flat surface in a room that can be made very dark. This could be a desk or dresser in the room, or a piece of wood (at least 40 centimeters [cm] by 15 cm) that can be taken into the room. Decide what surface you will use for assembling your spectrophotometer.
    1. When you test the spectrophotometer, cover the room's windows and any openings completely so that outside light does not come in. (Why do you think stray light might cause problems with collecting accurate data?)
  2. On the assembly surface you select, tape the diffraction grating using the transparent tape, as shown in Figure 4 below.
    1. Put one strip of tape on either side of the grating, propping it up so that it is perpendicular to the surface.
    2. Try to position the tape so that it does not block the central area of the grating (the part surrounded by cardboard).
    3. Make sure that the grating is stable and not wobbly.
    4. Once it is positioned, look around through the grating at a light source. Do you see a color spectrum?
Diffraction grating taped perpendicular to the surface of the base.
Chemistry science project
Figure 4. On the assembly surface, tape the diffraction grating so that it is stable and perpendicular to the surface.
  1. Slip the battery between the two prongs on the white LED bulb, as shown in Figure 5 below, and tape the two together using electrical tape.
    1. The slightly longer LED prong should be on the "+" side of the battery.
    2. If the bulb does not light up, trying moving the battery and bulb around slightly. If it still does not light up, you may need a new LED bulb or battery.
    3. Use a strip of electrical tape to tape the LED and battery together. Make sure the bulb remains lit after taping it to the battery.
Coin battery slipped between the prongs on the white LED light bulb.
Chemistry science project
Figure 5. Slip the battery (enlarged in this photo) between the two prongs on the LED bulb and adjust it so that the LED lights up.
  1. Position the LED-battery apparatus (the LED taped to the battery) at least 30 cm away from the diffraction grating, on top of its own small base (a small piece of wood or polystyrene that is 2 cm thick, or a baseplate), as shown in Figure 6 below.
    1. The LED-battery apparatus should not be in direct line with the diffraction grating, but should be off to the side a little. Position the LED-battery apparatus by looking through the diffraction grating and moving the LED-battery apparatus until the line of colors that comes through the diffraction grating is roughly in the center of the grating.
    2. When you finish adjusting the position of the LED-battery apparatus and its small base, tape the base to the main surface of the spectrophotometer, as shown in Figure 6. Make sure the base is securely in place. Do not tape the LED-battery apparatus to the base yet.
LED-battery apparatus positioned about 30 cm from the diffraction grating.
Chemistry science project
Figure 6. On its own small base (a piece of wood in this photo), position the LED-battery apparatus at least 30 cm away from the diffraction grating and off to the side a little so that the line of colors coming through the diffraction grating is in the middle of the diffraction grating.
  1. If you have to leave your spectrophotometer unattended for a few minutes, untape and separate the LED-battery apparatus so that the light is not lit, draining the battery while you are away. (It can be unsafe to leave the LED-battery apparatus unattended.)

Testing Your Samples

Now that you have assembled your spectrophotometer, you can test some samples. To do this, you will create different colored liquids using food colors, then place the liquids in front of the LED-battery apparatus and use the camera on your cell phone to take pictures of the spectra that come through the diffraction grating.

  1. 1. In a cup, add 5 mL or 1 teaspoon (tsp.) of water and 1 drop of a food color. Repeat this using the primary colors (blue, red, and yellow) and any other food colors you want to use for testing purposes.
    1. Swirl each cup gently to mix it.
  2. 2. Carefully pour each diluted food color into a cuvette. Fill each cuvette nearly to the top, as shown in Figure 7 below.
    1. You may want to use a medicine dropper to make filling the cuvette easier.
    2. When handling the cuvettes, try not to touch the smooth sides, but instead hold the cuvettes by the sides with the vertical grooves. Fingerprint smudges on the smooth sides may affect your results.
  3. Fill one cuvette with plain water. This will be your reference sample.
Cuvettes with diluted yellow, red, green, or blue food color.
Chemistry science project
Figure 7. Pour the diluted food color samples into cuvettes, being careful not to touch the smooth sides of the cuvettes. Fill one cuvette with water (far left). This will be your reference sample.
  1. Take your samples to the room where your spectrophotometer is assembled and set them nearby.
    1. If you disassembled the LED-battery apparatus, reassemble it and position it as you did in the "Assembling the Spectrophotometer" section (steps 3 and 4).
  2. Cover any windows and close any doors to prevent as much outside light as possible from coming in.
  3. Place your reference sample (the cuvette with only water) in front of the LED-battery apparatus, as shown in Figure 8 below.
    1. Position the cuvette so that the light is coming through a smooth side of the cuvette (a side that does not have vertical grooves).
Cuvettes with water (reference sample) in front of the LED-battery apparatus.
Chemistry science project
Figure 8. Place your reference sample (the cuvette with water only) in front of the LED-battery apparatus on your spectrophotometer.
  1. Turn off the lights in the room and adjust the position of your reference sample so that you can see the spectrum through the diffraction grating. The spectrum should look similar to the one in Figure 9 below.
    1. You may also need to adjust the position of the LED-battery apparatus.
Example color spectrum (using a sample of water only).
Chemistry science project
Figure 9. Adjust the position of your reference sample and LED-battery apparatus so that you can clearly see a spectrum (similar to this one) through the diffraction grating. (Your spectrum may be flipped so that the red is on the left and the blue is on the right, depending on how the diffraction grating is oriented. The orientation of the spectrum will not affect the results of your analysis.)
  1. Position your cell phone on the other side of the grating, as shown in Figure 10 below, so that you can clearly see the spectrum using your phone's camera.
    1. You may need to adjust the position of the LED-battery apparatus.
Setup of the cell phone spectrophotometer showing all components in place.
Chemistry science project
Figure 10. With your sample positioned in front of the LED-battery apparatus, position your cell phone's camera so that you can clearly photograph the color spectrum from the diffraction grating.
  1. Once you finish adjusting your setup, keep everything in place so that your conditions are consistent for each sample.
    1. Tape the LED-battery in place on its small base.
    2. Use a pencil to mark the exact position of the cuvette. (Outline where the base of the cuvette touches the surface of the spectrophotometer.)
    3. Re-check that the spectrum still looks clear on the camera of your cell phone.
  2. Take three pictures of each sample, including the reference sample.
    1. Make sure not to move your cell phone or any part of the spectrophotometer when taking pictures of the spectrum of each different sample. It is important that all conditions remain the same so that you can accurately compare the colored samples to the reference sample.
    2. Taking three images of each sample helps ensure that your results are accurate and reproducible. You may notice some differences between the images you take of the same sample.
    3. In your lab notebook or a scrap piece of paper, write the order in which you imaged your samples so that you will know later which pictures correlate to which samples.
  3. Set your samples aside, but do not throw them away yet. You may want to do further testing with them.
  4. Upload the pictures you took to a computer.

Analyzing Your Samples Using the Cell Phone Spectrophotometer Software Program

Now that you have collected sample data using your spectrophotometer, you can analyze your data using a software program. The program requires some fine-tuning time and playing around with to optimize your results.

  1. Download the cell phone spectrophotometer software program from http://www.asdlib.org/onlineArticles/elabware/Scheeline_Kelly_Spectrophotometer/CPSUpload.ZIP.
    1. Extract the compressed (zipped) folders.
    2. You can also download the program with Roman character sets from here: http://scheeline.scs.illinois.edu/~asweb/CPS/
    3. You will need to use a computer that can run Windows® software to use this program.
  2. Run the program by opening the CellPhoneSpec.exe file.
  3. On the top of the program screen, navigate through the computer to locate an image of a sample you want to analyze.
    1. Start with an image of a blue food color sample.
    2. The picture should show up on the left side of the screen.
  4. Move the scroll bars around until you can see the spectrum, as shown in Figure 11 below.
    1. If you cannot see the entire spectrum (it is too large to fit on the screen), you will need to resize your pictures so that they fit. You can resize them in a program such as Microsoft® Picture Manager or Paint.
    2. Save the resized picture and open it again, as you did in step 3.
  5. On the middle of the program screen, navigate through the computer to locate an image of your reference sample. Move the scroll bars around until you can see the spectrum.
    1. Again, if you cannot see the entire spectrum, you will need to resize your pictures.
Cell phone spectrophotometer program with samples uploaded.
Chemistry science project
Figure 11. Upload your pictures to the computer program, loading a colored sample on the left side and your reference sample (water only) on the right side. You may need to resize your images (using another program) so that they fit in the viewing area.
  1. Define the blue and red ends of the blue food color sample and reference sample by clicking on them.
    1. Click on the blue end of the spectrum of the blue food color sample. In the pop-up box, define the clicked point as "Blue End of Spectrum."
    2. Click on the red end of the spectrum of the blue food color sample. Define the clicked point as "Red End of Spectrum." The program should then draw a small green line across the spectrum.
    3. Repeat steps 6a to 6b on the reference sample.
    4. Your samples should now look like the ones in Figure 12 below, with a green line going through each spectrum.
Cell phone spectrophotometer program with samples loaded and ends defined.
Chemistry science project
Figure 12. After you click on the ends of each sample's spectrum and define the ends (as either the blue or red end), the program will draw a green line across each spectrum. The program will collect and analyze data from this line.
  1. Make an absorption spectrum of your blue food color sample.
    1. Under the program's "Plot Trace Selection" on the left side of the screen, select "Absorbance." Under "Abscissa Selection" select "Wavelength (nm)." Then click the button marked "Make Plot Compute T Compute A."
    2. By clicking on the y-axis and using the buttons circled in yellow in Figure 13 below, adjust the y-axis so that the graph fits on the screen and is stretched out along the y-axis as much as possible, as shown below.
Cell phone spectrophotometer program showing how to make absorption spectra.
Chemistry science project
Figure 13. Make an absorption spectrum of your colored samples by selecting "Absorbance" and "Wavelength (nm)" and then clicking on "Make Plot Compute T Compute A." You will probably need to adjust the y-axis so that the graph is stretched out along the y-axis as much as possible. This can be done using the buttons circled in yellow and clicking on the y-axis.
  1. You will probably see that on either end of the x-axis of the graph (which is the wavelength in nm), there is an apparent sharp increase in absorbance (the y-axis). In Figure 13 this starts around 420 nm and again at 640 nm. These increases in absorbance should be ignored for the purposes of this project by changing the x-axis to exclude these peripheral data points, as shown in Figure 14 below.
    1. Again, adjust the y-axis so that the data is stretched out along the y-axis as much as possible.
    2. The apparent increase in absorbance on either end of the x-axis is due to a camera's inability to adequately sense light toward the ultraviolet or infrared regions of the spectrum. As such, these apparent increases in signal are artifacts; in other words, they are not real data and can safely be ignored.
Cell phone spectrophotometer program showing absorption spectrum.
Chemistry science project
Figure 14. This is an adjusted and optimized absorption spectrum of a blue food color sample. This specific blue food color sample contains federal Food, Drug, and Cosmetic (FD&C) dye blue #1. There is a clear absorbance peak around 590 nm to 610 nm, which is at least 20 nm off from the expected peak of 630 nm for FD&C blue #1.
  1. Do you see a clearly defined peak on your graph, an area where the absorbance is distinctly higher than other points? If so, what is the wavelength (nm) of the point at which the peak occurs? For example, for the blue food color sample in Figure 14 a peak occurs around 590 nm to 610 nm. This is the wavelength of the maximum absorbance for this sample.
    1. For a blue food color sample, the peak should be around 610 to 630 nm, depending on the exact FD&C dye used. (FD&C dyes are synthetic food dyes approved for use in the United States by the Food and Drug Administration [FDA].) To figure out which specific blue dye is in your blue food color samples, look at the "Ingredients" listed on the packaging.
    2. See Table 1 below for the expected maximum absorbance of common FD&C dyes. Based on their color, why do you think these dyes have the maximum absorbance wavelengths that they do?
    3. The peak you observe may be as much as 30 nm away from the expected maximum absorbance of each dye.
    4. Some food color samples may contain multiple distinct peaks, depending on which dyes are in the samples. For example, if two dyes are used to make a certain food color, then two peaks may be observed, one for each dye.
FD&C Dyes Wavelength (nm) of Maximum Absorbance
Blue #1 630
Blue #2 610
Red #3 527
Red #40 502
Yellow #5 428
Yellow #6 484
Table 1. The different FD&C dyes, which are used in food colors, have certain expected wavelengths of maximum absorbance.
  1. If you cannot clearly see a large peak in the expected area, like the one shown in Figure 14 above, go to the "Optimizing and Troubleshooting" section below.
  2. How similar is the absorption spectrum of your blue food color sample to an ideal one for blue dye, such as the one shown in Figure 3 in the Introduction? How do you think you could make your absorption spectrum more similar to the ideal one?
    1. Hint: Read the "Optimizing and Troubleshooting" section for tips on how to make your absorption spectrum more accurate.
  3. Spend some time exploring the other options under "Plot Trace Selection" of the program.
    1. For each of the options, such as "Intensity (Both)," select it and then click on the "Make Plot Compute T Compute A" button to generate a graph of the data. What do you think the intensity graphs reveal about your samples and your cell phone camera?
  4. You can use your data to make graphs of absorbance versus wavelength and of transmittance versus wavelength. How do you expect the absorbance and transmittance graphs to be related?
    1. Click on the "Make Plot Compute T Compute A" button and then click on "Generate CSV File for Excel." Save the Excel file and open it.
    2. In Excel, make graphs of absorbance versus wavelength and of transmittance versus wavelength.
    3. Based on your graphs, how do transmittance and absorbance appear to be related?
  5. Once you finish analyzing your blue food color sample (and have looked at all three pictures you took of the sample), repeat steps 3 to 13 with your other food color samples. You can keep the same reference sample picture loaded.
    1. For each food color sample, look at Table 1 to determine the approximate wavelength of the maximum absorbance peak.
    2. Note that, depending on the exact yellow dyes in your samples, the absorption spectrum for the yellow food color samples may not be able to show the wavelength of maximum absorbance, for reasons discussed in step 8.

Troubleshooting and Optimizing Your Results

A large part of this project involves improving your spectrophotometer and the results you achieve using it. In this part of the project we will show you how to start doing this.

  1. The first thing you will want to check is whether your pictures are overexposed (some of the spectrum is white), which is easy to do and can make your pictures unusable in the computer program. An example of an overexposed spectrum is shown in Figure 15 below.
  2. Overexposed picture of a color spectrum, showing white where it should be blue.
Chemistry science project
    Figure 15. If a picture of a spectrum is overexposed, such as the picture here (the blue part of the spectrum contains white), it may be unusable in the program. Adjustments will need to be made to the spectrophotometer setup to eliminate any overexposure of the spectrum.
    1. If any part of your spectrum pictures are overexposed, and/or you cannot clearly see blue, green, and red, you should adjust the position of the LED-battery apparatus until the spectrum is clearer and not overexposed. Specifically, you may need to tilt the LED-battery apparatus, as shown in Figure 16 below, and move it back, farther away from the sample, so that less light goes through the sample.
Cuvette with water (reference sample) in front of the tilted LED-battery apparatus.
Chemistry science project
Figure 16. If your spectrum pictures look overexposed, you may need to tilt the LED-battery apparatus, as shown here, and move it back, farther away from the sample, to decrease the amount of light that reaches the camera.
  1. If your spectrum pictures are not overexposed, the easiest way to improve the absorption spectra of your samples (which you made in the "Analyzing Your Samples Using the Cell Phone Spectrophotometer Software Program" section, step 7) is by adjusting where the green lines run across your spectra. Start by creating an absorption spectrum of one of your samples (follow steps 2 to 8).
    1. You can click anywhere on a spectrum to reassign the red and blue ends of the spectrum. How does reassigning the ends of the spectrum (and then clicking on "Make Plot Compute T Compute A" button) change how the absorption spectrum looks?
    2. When assigning the ends of a spectrum, be sure that they are in similar places for both the food color sample and the reference sample. These two samples are compared to each other to generate the data, so they each need to compare similar points on the color spectrum to generate accurate absorption spectra.
    3. The entire length of the green line is used to generate the absorption spectrum, not just the two ends, so make sure that the line runs along similar parts of each spectrum.
    4. Look back at Figure 10 above and try to assign the ends of your spectra in similar locations.
    5. Figure 17 below was created using the same sample images that were used in Figure 12, but different parts of the sample spectra were designated as the ends. Because of the poor placement of the ends, the resultant absorption spectrum has no clear peak at the expected wavelength.
An example of how ends of spectra should not be defined in the cell phone spectrophotometer program.
Chemistry science project
Figure 17. Because of the poor labeling of the ends of the spectra in these samples, the resultant absorption spectrum has no clear peak at the expected wavelength.
  1. "Noise," small changes in the absorbance, can also be reduced by changing the "Spectrum Width (Pixels)" option (near the bottom right corner of the program).
    1. Adjust it from 1 to 10. How does this affect how the resultant absorption spectrum looks?

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Variations

  • You can use the cell phone spectrophotometer you made for this project to investigate dyes in other liquids. For example, you could test samples of different colored fruit juices or drink mixes. If you use drink mixes, dilute each drink mix powder in water to be the same concentration (such as 5 grams in 100 mL of water; the packaging usually says how many grams of powder it contains). Are the maximum absorbance wavelengths what you expect them to be? If there are multiple peaks, can you explain why this might be? If specific dyes are listed as ingredients, do you see distinctly the corresponding peaks?
  • Another way that you can investigate multiple dyes in a sample is through paper chromatography. Devise a way to examine the samples you investigated in this project using paper chromatography. For some chromatography projects, see:
  • Plants contain a variety of pigments that you could use your cell phone spectrophotometer to investigate. Collect differently colored flowers, plants, fruits, and vegetables and blend each of them in water to create differently colored solutions. Filter the solutions to remove any large particles. Investigate them with your spectrophotometer. Do you see absorbance peaks where you expect them? If the samples have multiple peaks, can you explain why this might be?
  • How sensitive is your cell phone spectrophotometer compared to a commercially available spectrophotometer? If you have access to a commercially available spectrophotometer, use the same color samples on it and compare the resulting absorption spectra. Are the absorption spectra very similar or very different?
  • Can you use your cell phone spectrophotometer to investigate the concentration of colored solutions? Devise a way to test this. Find information about the Beer-Lambert law and determine whether your spectrophotometer supports it.

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Chemist

Everything in the environment, whether naturally occurring or of human design, is composed of chemicals. Chemists search for and use new knowledge about chemicals to develop new processes or products. Read more
physics teacher helping student model a nanostructure

Physics Teacher

Our universe is full of matter and energy, and how that matter and energy moves and interacts in space and time is the subject of physics. Physics teachers spend their days showing and explaining the marvels of physics, which underlies all the other science subjects, including biology, chemistry, Earth and space science. Their work serves to develop the next generation of scientists and engineers, including all healthcare professionals. They also help all students better understand their physical world and how it works in their everyday lives, as well as how to become better citizens by understanding the process of scientific research. Read more
chemistry teacher conducting classroom demonstration

Chemistry Teacher

When you hear the word chemicals, you might think of laboratories and scientists in white coats; but actually, chemicals are all around you, as well as inside of you. Everything in the world is made up of chemicals, also known as matter, or stuff that takes up space. Chemistry is the study of matter—what it is made of, how it behaves, its structure and properties, and how it changes during chemical reactions. Chemistry teachers are the people who help students understand this physical world, from the reactions within our own bodies to how soaps and detergents work and why egg proteins can keep a cookie from crumbling. They prepare the next generation of scientists and engineers, including all healthcare professionals. They also help also students develop scientific literacy. Read more