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A few questions about light, solar panels, and electric currents.

  1. Jan 25, 2012 #1
    Hello, my name is Stefan and I am a twelfth grade high school student working on an extracurricular project which I will present and be ranked(individually; non-competitively) on. I hope to achieve the best possible score and plan to put a lot of work into it. I have a little over a month, which I will spend probably 40-50 hours working on this project. I seem to be on the right track, but I want to make sure I understand everything conceptually with the most accuracy possible so that my presentation represents the facts correctly. Unfortunately, the only physics course offered at my school is a college preparation course and consists of very slow-paced concepts in mechanics(all algebra/trigonometry based), so a lot of these concepts involved in my experiment come from other science classes I have taken(two years of Chemistry; three years of Biology - including AP Biology) and knowledge I must self-teach/be taught by my physics teacher, whom is sponsoring and helping me gather the materials required for the experiment. Math-wise I am currently in AP Calculus AB and have a hang of derivatives, but have yet to do integrals(which I plan to teach myself.) I have alright abilities in pre-calculus, but the trigonometry course, and my quite poor Algebra II class, covered predominately exponential, logarithmic, and trigonometric functions, omitting specific details of polynomials and quadratics. We also didn't go over polar coordinates, parametric equations, sequences, conic sections, and matrices. A few of those concepts we touched a bit on, but nothing as extensive as what is in the pre-calculus book I am using to teach myself. I'm sure my physics teacher will help me with any math, although I hope to use the most advanced and appropriate mathematics in my tool-set to make the interpretation of data as thorough as possible. So any direction on that end would be much appreciated. Anyway, sorry for the long introduction, I'll proceed to the actual project description/questions.

    The main goal of the project is to see how the electric current of a solar panel changes based on different wavelengths and different light sources(the current ideal being sunlight.) We have a solar panel(of which I don't know the details), and colored filters. I hope to gain all of the knowledge I can about circuits and the transfer of energy through the photoelectric effect, but I am having difficulty finding answers to some very specific questions. My resources are two detailed algebra-based physics textbooks, Feynman's lectures, and the internet of course. I am considering reading sections that correspond to this from the Feynman's lecture set, which I use to understand mechanics concepts better. I assume the predominance of it would be in the second volume, but I'm unsure which chapters would help me understand the most. It seems like everything in that volume could be useful.

    1. How specifically do electrons receive energy from a photon? I understand it at the most basic level taught in my chemistry class, a photon "hits" the electron transferring its energy and exciting the electron from its ground state. This causes a current to be produced by the valence electrons of the atom, specifically in conductors where there is freedom to move. I want to know how the energy is transferred though. Since the photon has the least energy possible(isn't that why it is called a "light quantum")which I assume depends on its wavelength/frequency. Basically I should drop the idea that photons transfer the electromagnetic force and see it more as photons are the electromagnetic force? If that is correct, then what happens to the photon after the energy is transferred? I want to think that it is "absorbed", yet I am not certain. If that is incorrect, then what exactly is a photon's involvement with the electromagnetic force?

    2. How much energy is transferred from the photon to the electron during this process? How much is usually loss(made unusable) through heat?

    3. Is there any good description on the internet which delineates the different types of solar panels in detail, the material they are composed of, and a detailed(as much as possible) explanation of how they work? If so, may you provide me with this link or various links.

    4. Which light sources should show the most noticeable differences in how they affect the energy output of the solar panel?

    5. How might I improve my project if I find myself to have more time to play with it, after I accomplish my targeted goals?

    6. What skills should I work on in order to improve my understanding? Specifically, which chapters of Feynman's lectures would be the best to study to gain a conceptual, mostly qualitative understanding? What textbooks/web resources will allow me to refine that qualitative understanding with a quantitative one, hopefully the most specific for my current mathematical abilities?

    Thank you very much for any help, and I hope my questions aren't too simple that they might be a burden to answer.

    Edit: Oh, unfortunately I believe I posted this in the wrong section. I should have read the guidelines first, I thought homework was specifically formal questions. Ok, I will wait until this is deleted then I will ask in the homework section. Sorry
    Last edited: Jan 25, 2012
  2. jcsd
  3. Jan 25, 2012 #2


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    1. Quanta doesn't mean "least" it simply refers to the fact that a photon can only transfer it's energy completely or not at all. The energy, once the photon is emitted, is carried with it and does not leak out or anything. Once it interacts with an electron and transfers energy to it the photon is gone completely, it no longer exists.
    A photon is considered to be an Electromagnetic Wave, not the actual force itself. Similarly you wouldn't call a water wave the water or force itself, but merely a wave. Consider this, if you charge an object with an electric charge it does not emit photons, it is simply charged and will attract oppositely charged objects.

    2. To my knowledge when a photon interacts with an electron, it is actually interacting with the atom as a whole and can transfer energy to both. However I'm not real sure on this.

    3. All of them work according to the same basic principles. Wikipedia might have enough information to explain the difference between the types.

    4. The only difference would be between different intensities and wavelengths that are being emitted between the light sources. You may just want to stick with a single light source since you are going to use color filters.

    5. If you have time I suggest experimenting with different setups and just see what happens. Different angles, intensities, etc. I'm sure you'll find something interesting.

    6. That really depends on how "deep" you want to go. Saying that the photons are absorbed by electrons which cause the electrons to gain energy and move along the circuit is basic, but still correct. I wouldn't worry about diving too deep into this area until you understand the basics and have your experiment set up and working.
  4. Jan 25, 2012 #3


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    Stefan10, Welcome to Physics Forums!

    As far as I understand them, the Forum Guidlines permit you to post this here since it is an "extracurricular project" and NOT homework.

    You have asked very important questions and seem to be on track to make a superb photovotaics project. I am looking for some references for you, and will post them later.
  5. Jan 25, 2012 #4


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    You don’t need to use a complete solar panel to do this experiment. A panel is an array of cells connected together for the purpose of powering a load. For your experiment one simple PV cell would be enough to do the experiments. You will definitely need a good quality Digital Multimeter to measure voltages and currents.

    I used the search terms “photovoltaic cells wavelength” on Google and came up with these:

    The objective is to determine the effect of light wavelength on the electrical output of photovoltaic cells with the goal of improving the efficiency of solar panels.


    2. This thread is from right here on Physics Forums: “On the relationship between wavelength and intensity of light to the electric power produced by a photovoltaic cell.”


    3. A good technical description of the factors that affect photovoltaic cell conversion efficiency:

    4. Here is a project called “Wavelength of Light that hits a Solar Panel” and is a complete description of a Science Fair project. Note that this one suggests using a prism in sunlight to produce the continuum of wavelengths over the entire spectrum. Using a narrow slit you could slowly scan your cell with the spectrum and record the current output.


    5. Here is a technical paper that introduces some sophisticated techniques of measuring the effects of different wavelengths on the output of the PV cell.

    “A comparison of two types of solar concentrators for use with standard silicon photovoltaic cells is provided. The first is spectral shifting luminescent concentrator that absorbs light in one spectral band and re-emits light at longer wavelengths where the absorption of standard silicon photovoltaic cells is more efficient. The second type is a holographic planar concentrator that selects the most useful bands of the solar spectrum and concentrates them onto the surface of photovoltaic cell.”

  6. Jan 25, 2012 #5


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    Great technical description from NASA answering several of your questions:


    This is from Norway. It is one of the best tutorial I have seen. Don’t let the mathematics scare you…there is plenty of information in plain English!

    2 Basic Principles of Photovoltaics
    2.1 Solar Radiation
    2.2 Solar Energy Converters
    2.3 Performances of a PV cell
    2.4 Work from a PV cell
    2.5 Effects of band gap and spectrum

    http://org.ntnu.no/solarcells/pages/Chap.2.php [Broken]
    Last edited by a moderator: May 5, 2017
  7. Jan 25, 2012 #6
    Thank you very much. I think I have a good conceptual basis to form upon now, with my current questions sufficiently resolved, and the resources provided are exactly what I need. I'll use them to produce a procedure and if I have any other ideas or questions that I can't work out myself or with the help of my physics teacher, I will return. Again, thank you!
  8. Feb 17, 2012 #7
    Hey I have a few questions.

    Is time relative and does every one experience time differently. I myself believe that time is relative and that we in fact live in the present but see the past. When we look at things we see them how they were,thats due to the fact that it takes time for light to hit an object and enter our eyes, its almost as if time self is an illusion. And if objects exists before light hits them then how is time measured, by existence, or by perception.
  9. Feb 17, 2012 #8


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    Welcome to PF GavinTodd!
    Unfortunately your question is completely off topic for this particular thread, but if you take your post and start a new thread we can discuss it there!
  10. Feb 23, 2012 #9
    I have a more concrete question now.

    So far, I have five filters with wavelengths in a single range each(none are combinations of colors) these are: "Red", "Blue", "Green", "Violet", and "Orange". Although each has a more specific wavelength range than the general spectrum attributed to each color and could be better described as discrete opposed to continuous when considered cumulatively.

    I have two voltmeters connected through a circuit with a resistor, one measuring the voltage and the other measuring the current produced by the photo-voltaic cell.

    The main purpose of the experiment is to measure the distinction of the rate of energy output(power) of the photo-voltaic cell depending on the wavelength. Unfortunately, the filters all have different transmissions. Although when choosing them I tried to pick the smallest range possible(based on the transmittance vs wavelength graphs.) My teacher and I think we would get far better results if we could accommodate for this transmittance difference further. Can anybody provide direction to how we can accommodate for this? Is there a sort of mathematical method or material we can use to help "even it out"?

    Again, thank you very much! All of the resources have helped me greatly to form the conceptual basis needed to progress.
    Last edited: Feb 23, 2012
  11. Feb 23, 2012 #10


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    If you know the transmittance of each filter, can you dim or brighten the light source to make up for any difference between the filters? For example, if your orange filter only lets 50% of its range through, and the green one lets 75% through, can you increase the intensity by 50% to account for the loss in light through the orange filter? Or dim it instead for the green one?
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