DOCSLIB.ORG

The Photoelectric Effect

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Photoelectric Effect PHOTOELECTRIC EFFECT The Photoelectric Effect In 1887 German physicist Heinrich Hertz discovered that electric charge is emitted from the surface of a metal body when illuminated with ultraviolet light. More careful investigation showed that electromagnetic radiation is able to release electrons from the surface of a metal. This phenomenon is now known as the photoelectric effect. Electron emission occurs only if the frequency of incident light exceeds the characteristic cut-off frequency of the particular metal. Importantly, the photoelectric effect cannot be explained in terms of classical physics with light modeled as a wave. Electric charge and discharge Here we explore the electric charging and discharging of an aluminium can, using ultraviolet light. Follow the steps and record your observations in the table below. Remove any dirt or build up of aluminium oxide on the can using the sandpaper provided. Place the aluminium can on the electroscope and transfer electric charge to the can using an ebonite rod. What type of electric charge is generated in this way? Illuminate the cleaned surface of the can with light from a torch. What do you notice? Using goggles, illuminate the same surface with ultraviolet (UV) light. What do you notice? Now use a glass rod to transfer electric charge to the aluminium can. What type of electric charge is generated in this way? Illuminate the cleaned surface of the can with light from a torch. What do you notice? Illuminate the same surface with ultraviolet light. What do you notice? Type of light Negative charge Positive charge Bright white light Dim white light Bright UV light Dim UV light Which particles of the metal do you think are being emitted as the can discharges? PAGE 1 / 8 PHOTOELECTRIC EFFECT An electric charge can be interpreted as an excess or a deficit of electrons. Charging with an ebonite rod causes an excess of electrons thereby producing a negative electric charge. When illuminated with ultraviolet light the aluminium can discharges, but this is not the case with torch light. It is apparent that ultraviolet light has a particular feature that the torch light lacks, or that ultraviolet light has more of ‘something’ than the torch light. When using the glass rod for the assignment a positive charge is produced due to a deficit of electrons. In this case no change in the electric charge of the can is detected with either the torch light or ultraviolet light. The negative charge on the can decreases as excess electrons are emitted. The UV light is therefore able to remove some of the electrons from the surface of the metal. Light intensity (which is the amount of light) and the colour of light both effect the ability of light to remove electrons in this way. The photoelectric effect: experimental equipment 1) Protective cover for the photocell 2) Light conducting tube: for LEDs 3) Nano-ammeter for photocurrent 4) Voltmeter for control voltage 5) Dial for adjustment of control voltage 6) Dial for fine adjustment of control voltage 7) Dial for setting light source intensity 8) Socket for the light source 9) Socket for the power supply 10) LEDs with cables • Connect the red light source to the equipment. What do you notice? What is the cause of the electric current generation? What is the source of the electrical power required to maintain the energy of the current? PAGE 2 / 8 PHOTOELECTRIC EFFECT The main part of the equipment is the photocell, whose light sensitive electrode (the cathode) is made of caesium. This cathode (the negative electrode) corresponds to the metal body within the equipment from which electrons are emitted. In the photoelectric effect, emitted electrons are called photoelectrons. When the cathode is illuminated using LED lights of different colours, a weak current can be observed passing through the photocell. This is called the photocurrent. The observation can be interpreted as the light removing electrons from the metal cathode, which then travel to the anode. (1) where is current, is charge and is time. Since maintaining an electrical current requires energy the energy of the incident light must transfer kinetic energy, , to the electrons (2) where is mass and is velocity. Adjust the control voltage in both the forward direction and the reverse direction. What do you notice? What factors affect the magnitude of the current? What does the magnitude of the current indicate about the photoelectrons? Why does the magnitude of the current decrease as the voltage is increased? PAGE 3 / 8 PHOTOELECTRIC EFFECT What does the control voltage produce in the vacuum tube between the electrodes? Where is the kinetic energy of the emitted electrons transferred to? The photoelectric cell is placed between the electrodes of an external variable voltage, the control voltage. It can be observed that this external voltage affects the magnitude of the photocurrent. If the voltage is positive (the cathode is negative) the photocurrent flows. If the voltage is negative (the cathode is positive) the photocurrent is decreased and for a certain voltage stops completely. The magnitude of electric current in the circuit (i.e. the photoelectrons flowing through the vacuum tube) can be regulated by the control voltage. Adjusting the control voltage changes the electric field opposing the motion of photoelectrons, and is found to decrease the current. As the reverse voltage, , increases the circuit current, , decreases. The control voltage generates an electric field in the equipment which affects the flow of photoelectrons. With a negative voltage between the electrodes the electric field acts as a ‘brake’, decelerating the electrons flowing from the cathode to the anode. When moving in an electric circuit against an electric field photoelectrons will do an amount of work (3) where is the reverse or ‘braking’ voltage and is the charge on an electron. • Search, by adjusting the control the voltage, for the value of at which the current is zero. What can we say about the motion of photoelectrons in this situation? Where is the kinetic energy of the emitted electrons transferred to? PAGE 4 / 8 PHOTOELECTRIC EFFECT When the voltage of the circuit is adjusted such that the electric current is zero, we can conclude that all (even the fastest) photoelectrons have been stopped. The kinetic energy of the photoelectrons, , is then matched by the work done, , against the electric field. We can show the calculation as: (4) (5) (6) where is the work done on a photoelectron by the electric field with control voltage and elementary charge . is the final kinetic energy of the photoelectron and is the initial kinetic energy of the photoelectron. The voltage at which the current is stopped is called the stopping voltage, . By measuring the stopping voltage we can determine the maximum kinetic energy of the photoelectrons, . The relationship between stopping potential and maximum kinetic energy of photoelectrons is (7) The interpretation of these results is that light striking the cathode gives the photoelectrons kinetic energy, this energy is sufficient to bring the electrons to the anode only if their kinetic energy is greater than the energy needed to work against the electric field. The stopping voltage of the emitted electrons with maximal kinetic energy is therefore equal to work done by the electron against the opposing electric field. Does the stopping potential depend on the light intensity? PAGE 5 / 8 PHOTOELECTRIC EFFECT When the current is reduced to zero, electrons are no longer arriving at the anode. By adjusting the intensity of light incident on the cathode we find that the magnitude of the current varies, however the voltage at which all the electrons can be stopped remains the same. Consider what your findings indicate about the interaction of light with the cathode material. • Repeat your measurements with other light sources, and record the results below. Wavelength of light Frequency of light Stopping voltage Maximum kinetic (nm) ( Hz) (V) energy of electrons ( J) What factors influence the value of the stopping voltages? What does this say about the energy of the photoelectrons? Where does this energy come from? What can we conclude about light on the basis of these results? PAGE 6 / 8 PHOTOELECTRIC EFFECT Varying the color of light (by changing the frequency of the radiation) produces similar results for all frequencies, with the exception that the value of the stopping voltage is different for each frequency. The stopping voltage depends on the frequency of light incident on the cathode and therefore the maximum kinetic energy received by the electrons also depends on the frequency of the incident light. It is evident that the energy of light is proportional to its frequency. • Plot the data obtained from measurements on a graph with on the y-axis and on the x-axis. The maximum kinetic energy of the electrons can be calculated from equation (7). What type of graph is produced by plotting these data points? What does this say about the relationship between the maximum kinetic energy of the photoelectrons and light frequency? • If possible, draw a line of best fit What does the value of the slope determine and what are the units? What is the physical meaning of the x-coordinate at the intercept on the x-axis? PAGE 7 / 8 PHOTOELECTRIC EFFECT From the graph, the frequency intercept can be interpreted as a threshold point below which the lower frequency radiation does not contain enough energy to eject an electron from the metal. This interpretation is supported by the earlier observations whereby the light from a torch was unable to remove electric charge from the charged can, while the UV light could. The intercept on the energy axis can be interpreted as the amount of energy an electron requires to escape from the sea of electrons.
Load more

Recommended publications
  • The Photoelectric Effect in Photocells Suggested Level: High School Physics Or Chemistry Classes
    The Photoelectric Effect in Photocells Suggested Level: High School Physics or Chemistry Classes LEARNING OUTCOME After engaging in background reading on electromagnetic energy and exploring the frequencies of various colors of light, students realize that it is useful to think of light waves as streams of particles called quanta, and understand that the energy of each quantum depends on its frequency. LESSON OVERVIEW This lesson introduces students to the photoelectric effect (the basic physical phenomenon underlying the operation of photovoltaic cells) and the role of quanta of various frequencies of electromagnetic energy in producing it. The inadequacy of the wave theory of light in explaining photovoltaic effects is explored, as is the ionization energies for elements in the third row of the periodic table. MATERIALS • Student handout • Roll of masking tape • Ball of yarn • Scrap paper SAFETY • There are no safety precautions for this lesson. TEACHING THE LESSON Begin by explaining the structure and operation of photovoltaic cells, covering the information in the student handout and drawing from the background information below. Stake off an area of the classroom in which about two-thirds of your students can stand. It could, for example, be bounded by tape on the floor. This area is to represent a photovoltaic cell. Have half of your students form a line dividing the area in half. They represent the electrons lined up on the p-side of the p-n junction. Stretch yarn from the n-type semiconductor to one student chosen to represent a light bulb and from that student to the p-type semiconductor.
    [Show full text]
  • Introduction to Photovoltaic Technology WGJHM Van Sark, Utrecht University, Utrecht, the Netherlands
    1.02 Introduction to Photovoltaic Technology WGJHM van Sark, Utrecht University, Utrecht, The Netherlands © 2012 Elsevier Ltd. 1.02.1 Introduction 5 1.02.2 Guide to the Reader 6 1.02.2.1 Quick Guide 6 1.02.2.2 Detailed Guide 7 1.02.2.2.1 Part 1: Introduction 7 1.02.2.2.2 Part 2: Economics and environment 7 1.02.2.2.3 Part 3: Resource and potential 8 1.02.2.2.4 Part 4: Basics of PV 8 1.02.2.2.5 Part 5: Technology 8 1.02.2.2.6 Part 6: Applications 10 1.02.3 Conclusion 11 References 11 Glossary Photovoltaic system A number of PV modules combined Balance of system All components of a PV energy system in a system in arrays, ranging from a few watts capacity to except the photovoltaics (PV) modules. multimegawatts capacity. Grid parity The situation when the electricity generation Photovoltaic technology generations PV technologies cost of solar PV in dollar or Euro per kilowatt-hour equals can be classified as first-, second-, and third-generation the price a consumer is charged by the utility for power technologies. First-generation technologies are from the grid. Note, grid parity for retail markets is commercially available silicon wafer-based technologies, different from wholesale electricity markets. second-generation technologies are commercially Inverter Electronic device that converts direct electricity to available thin-film technologies, and third-generation alternating current electricity. technologies are those based on new concepts and Photovoltaic energy system A combination of a PV materials that are not (yet) commercialized.
    [Show full text]
  • The History of Solar
    Solar technology isn’t new. Its history spans from the 7th Century B.C. to today. We started out concentrating the sun’s heat with glass and mirrors to light fires. Today, we have everything from solar-powered buildings to solar- powered vehicles. Here you can learn more about the milestones in the Byron Stafford, historical development of solar technology, century by NREL / PIX10730 Byron Stafford, century, and year by year. You can also glimpse the future. NREL / PIX05370 This timeline lists the milestones in the historical development of solar technology from the 7th Century B.C. to the 1200s A.D. 7th Century B.C. Magnifying glass used to concentrate sun’s rays to make fire and to burn ants. 3rd Century B.C. Courtesy of Greeks and Romans use burning mirrors to light torches for religious purposes. New Vision Technologies, Inc./ Images ©2000 NVTech.com 2nd Century B.C. As early as 212 BC, the Greek scientist, Archimedes, used the reflective properties of bronze shields to focus sunlight and to set fire to wooden ships from the Roman Empire which were besieging Syracuse. (Although no proof of such a feat exists, the Greek navy recreated the experiment in 1973 and successfully set fire to a wooden boat at a distance of 50 meters.) 20 A.D. Chinese document use of burning mirrors to light torches for religious purposes. 1st to 4th Century A.D. The famous Roman bathhouses in the first to fourth centuries A.D. had large south facing windows to let in the sun’s warmth.
    [Show full text]
  • Polymeric Materials for Conversion of Electromagnetic Waves from the Sun to Electric Power
    polymers Review Polymeric Materials for Conversion of Electromagnetic Waves from the Sun to Electric Power SK Manirul Haque 1, Jorge Alfredo Ardila-Rey 2, Yunusa Umar 1 ID , Habibur Rahman 3, Abdullahi Abubakar Mas’ud 4,*, Firdaus Muhammad-Sukki 5 ID and Ricardo Albarracín 6 ID 1 Department of Chemical and Process Engineering Technology, Jubail Industrial College, P.O. Box 10099, Jubail 31961, Saudi Arabia; [email protected] (S.M.H.); [email protected] (Y.U.) 2 Department of Electrical Engineering, Universidad Técnica Federico Santa María, Santiago de Chile 8940000, Chile; [email protected] 3 Department of General Studies, Jubail Industrial College, P.O. Box 10099, Jubail 31961, Saudi Arabia; [email protected] 4 Department of Electrical and Electronics Engineering, Jubail Industrial College, P.O. Box 10099, Jubail 319261, Saudi Arabia 5 School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen AB10 7QB, Scotland, UK; [email protected] 6 Departamento de Ingeniería Eléctrica, Electrónica, Automática y Física Aplicada, Escuela Técnica Superior de Ingeniería y Diseño Industrial, Universidad Politécnica de Madrid, Ronda de Valencia 3, 28012 Madrid, Spain; [email protected] * Correspondence: [email protected]; Tel.: +966-53-813-8814 Received: 10 February 2018; Accepted: 6 March 2018; Published: 12 March 2018 Abstract: Solar photoelectric energy converted into electricity requires large surface areas with incident light and flexible materials to capture these light emissions. Currently, sunlight rays are converted to electrical energy using silicon polymeric material with efficiency up to 22%. The majority of the energy is lost during conversion due to an energy gap between sunlight photons and polymer energy transformation.
    [Show full text]
  • Determination of the Main Parameters of the Photovoltaic Solar Module
    E3S Web of Conferences 191, 01004 (2020) https://doi.org/10.1051/e3sconf/202019101004 REEE 2020 Determination of the main parameters of the photovoltaic solar module Baydaulet A.Urmashev1, Murat Kunelbayev2*, Almas N.Temirbekov3, Syrym Kassenov4, Zhadra Zhaksylykova5, Farida Amenova6 1,3Department of Computer Science, Kazakh National University named after al-Farabi, Almaty, Republic of Kazakhstan 2Institute Information and Computational Technologies CS MES RK, Almaty, Republic of Kazakhstan 4Faculty of Mechanical Mathematics, al-Farabi Kazakh National University, Almaty, Kazakhstan 5Abay Kazakh National Pedagogical University, Almaty, Republic of Kazakhstan 6S. Amanzholov East Kazakhstan State University, Department of Mathematics, Faculty of Science and Technology Ust-Kamenogorsk, Republic of Kazakhstan Abstract. This article deals with the determination of the main operating parameters of a photovoltaic solar module. In laboratory tests, the study of the dependence of current, voltage and power on time and density of solar radiation, as well as monitoring of environmental parameters: temperature and humidity of the outside air. Analysis of the test results shows that a photoelectric module with an installed capacity of 800 W and a total battery capacity of 800 Ah provides the electric power industry with a daily consumption of 2.0 ... 2.2 kWh. The discharge time of the battery varies from 11.7 to 3.5 hours when the average electric load of the consumer changes from 300 to 1000 watts. homogeneous structure. The basis for the formation of cells that are suitable silicon-sized blocks. 1 Introduction They are cut into plates whose thickness is Solar cells in the production of electricity from about 0.3 mm.
    [Show full text]
  • WO 2018/222569 Al 06 December 2018 (06.12.2018) W !P O PCT
    (12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (19) World Intellectual Property Organization International Bureau (10) International Publication Number (43) International Publication Date WO 2018/222569 Al 06 December 2018 (06.12.2018) W !P O PCT (51) International Patent Classification: KR, KW, KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, C01B 3/00 (2006.01) MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM, PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SA, (21) International Application Number: SC, SD, SE, SG, SK, SL, SM, ST, SV, SY,TH, TJ, TM, TN, PCT/US20 18/034842 TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW. (22) International Filing Date: (84) Designated States (unless otherwise indicated, for every 29 May 2018 (29.05.2018) kind of regional protection available): ARIPO (BW, GH, (25) Filing Language: English GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, TZ, UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, TJ, (26) Publication Langi English TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK, (30) Priority Data: EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV, 62/5 13,284 31 May 2017 (3 1.05.2017) US MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM, 62/5 13,324 31 May 2017 (3 1.05.2017) US TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, 62/524,307 23 June 2017 (23.06.2017) US KM, ML, MR, NE, SN, TD, TG).
    [Show full text]
  • DSSC) Lecture for ENG 230
    Dye Sensitized Solar Cell (DSSC) Lecture for ENG 230 May be 50 minutes of 3 hr lab.- would follow 30 minutes of cell assembly INTRODUCTION Economics Solar cells absorb some of the photons from sunlight and convert it to a useable amount of direct current electricity. The costs of solar power have been declining steadily and eventually will be competitive with traditional dirty sources of power which are currently contributing to climate change. The solar power falling on about one square mile is around 3 gigawatts, so a 30% efficient cell would produce 1 gigawatt per sq mile, the same as a nuclear plant. The cost of solar is not just in the cells but in the structure to hold the cells in all weathers, and in some cases to orient the cells to the sun. However, the cell cost is significant, and the DSSC combines the natural photovoltaic effect of pigments with nanotechnology to make it competitive with the silicon cells which are in production. The Photovoltaic Effect The photovoltaic effect is the creation of voltage in a material upon exposure to light. Though the photovoltaic effect is directly related to the photoelectric effect, they are different processes. In the photoelectric effect, electrons are ejected from a material's surface upon exposure to radiation. The photovoltaic effect differs in that electrons are transferred between different bands (i.e., from the valence to conduction bands) within the material, resulting in the buildup of voltage between two electrodes. Illuminating the material creates an electric current as excited electrons and the remaining holes are swept in different directions by the built-in electric field of the depletion region.
    [Show full text]
  • The Cavity QED Induced Thermophotovoltaic Effect
    Asian J. Energy Environ., Vol. 4, Issues 3-4, (2003), pp. 163-183 The Cavity QED Induced Thermophotovoltaic Effect T. V. Prevenslik 14B, Brilliance Court, Discovery Bay, Hong Kong Email: [email protected] (Received : 15 October 2003 – Accepted : 26 November 2003) Abstract : Thermophotovoltaic (TPV) devices comprise a heater separated from a photocell by a microscopic gap. As the gap is slowly reduced, the photocell current increases while the temperature drops suggesting an underlying thermal mechanism. Conversely, a non-thermal mechanism is indicated since the current remains in phase with rapid gap changes that are faster than the response time of the heater. Both slow and rapid TPV responses may be explained by a theory based on the modification of thermal blackbody (BB) radiation by the gap as a quantum electrodynamics (QED) cavity, the theory called the cavity QED induced TPV effect. By varying the gap, the electromagnetic (EM) resonance of the QED cavity may be adjusted from infrared (IR) to vacuum ultraviolet (VUV) frequencies. At typical heater temperature, the thermal kT energy of the atoms is emitted in the far IR, but the photocells are only sensitive over a small range of frequencies in the near Copyright © 2003 by the Joint Graduate School of Energy and Environment 163 T. V. Prevenslik IR. Thus, for large gaps having EM resonance beyond the far IR, the gap does not modify the BB spectrum, and therefore the photocell current is negligible because of the lack of near IR photons. But if the gap resonance is adjusted to the near IR, the far IR radiation undergoes a frequency up-conversion to produce near IR photons that dramatically increase the photocell current, the frequency up-conversion a consequence of conserving EM energy within cavity QED constraints.
    [Show full text]
  • A Potential Pathway to High Efficiency Concentrated Solar Power
    Energy & Environmental Science View Article Online PAPER View Journal | View Issue Thermophotovoltaics: a potential pathway to high efficiency concentrated solar power† Cite this: Energy Environ. Sci., 2016, 9,2654 Hamid Reza Seyf*a and Asegun Henryabc A high temperature thermophotovoltaic (TPV) system is modeled and its system level performance is assessed in the context of concentrated solar power (CSP) with thermal energy storage (TES). The model includes the treatment of the emitter and the heat transfer fluid that draws thermal energy from the TES, which then allows for the identification and prioritization of the most important TPV cell/ module level properties that should be optimized to achieve maximum performance. The upper limiting efficiency for an idealized system is then calculated, which shows that TPV with TES may one day have the potential to become competitive with combined cycle turbines, but could also offer other Received 12th May 2016, advantages that would give CSP an advantage over fossil based alternatives. The system concept is Accepted 4th July 2016 enabled by the usage of liquid metal as a high temperature heat transfer and TES fluid. The system DOI: 10.1039/c6ee01372d concept combines the great economic advantages of TES with the potential for low cost and high performance derived from TPV cells fabricated on reusable substrates, with a high reflectivity back www.rsc.org/ees reflector for photon recycling. Broader context Current approaches to concentrated solar power (CSP) rely on the same heat engines as fossil fuels, and thus the only way CSP can become cost competitiveisif the cost of collecting and storing high temperature heat from the sun can become less expensive than the heat delivered by fossil fuels.
    [Show full text]
  • Senior Project: Solar Bench
    1 Senior Project: Solar Bench Submitted by: Meshari Alharbi, Electrical Engineering Sponsored by University of Evansville Submitted to: DR. Christina Howe Project advisor: Dr. Mohsen Lotfalian Date and Place: March 25, 2017 2 Acknowledgements: I wish to express my gratitude to Dr. Lotfalian for advising my project, and Mr. Jeff Cron for his help with acquiring parts support, guidance and encouragement, without which this project wouldn’t have come forth. I would like also to express my gratitude to the staff of the Electrical Engineering Department for their support during the project. 3 Table of Contents: I. Introduction II. Problem Definition III. Design Approach . Main parts . IV. Safety and Environment V. Standards VI. Expected Result VII. References VIII. Appendix 4 Table of Figures: Figure 1: PV system Demo Figure 2: Arduino Nano layout Figure 3: MP1584EN Buck converter Figure 4: MP1584EN buck converter performance Figure 5: Schematics for the charge controller Figure 6: Final demo of the solar bench Table of tables: Table 1: Solar panels specification Table 2: Charge controller specifications Table 3: Charge controller parts coast 5 Solar Bench I. Introduction: In today’s technology, many products are being redesigned to be more efficient. As more products become more portable, the demand for portable power increases. Due to the limitations of fossil fuels, solar energy is becoming more popular as the renewable energy source that could change the future. The world depended on oil and gas as the main sources of energy, which damage the environment in many aspects. Some Engineers are trying to make energy without effecting the environment (renewable energy), for example oxygen, fresh water, solar, timber, and biomass energy.
    [Show full text]
  • T12. the Photoelectric Effect and Planck's Constant
    EXPERIMENT 12 THE PHOTOELECTRIC EFFECT AND PLANCK'S CONSTANT White light that is passed through various filters illuminates the photoelectric surface of a phototube causing photoelectrons to be emitted with energies dependent upon the energy of the light hitting the surface. The electrons then flow through the phototube to the collector and constitute a current flow. A voltage called the stopping voltage or stopping potential is applied to halt the flow of photoelectrons. If the frequencies or wavelengths of the incoming light and the corresponding stopping voltages are known, then the value of Planck's Constant can be found. THEORY When light strikes a metallic surface, electrons are emitted from the surface. This effect is called the photoelectric effect. The emitted electrons, called photoelectrons, have varying kinetic energies that are primarily dependent upon the frequency of the light that strikes the surface. (See Figure 1.) Figure 1. Light strikes a metallic surface and causes the emission of photoelectrons. In 1905 Albert Einstein was able to provide an explanation of the photoelectric effect. He proposed that light acts like a particle having energy equal to nf, where n is Planck's constant and f is the frequency of the incident light. These particles of light, called photons or quanta collide with and transfer energy to the electrons in the metal. The emitted electrons then use part of this energy to migrate to the surface of the metal and part to free themselves from the electrostatic attraction of the metallic surface; the remainder goes into the kinetic energy of the electrons. For those electrons at the surface of the metal, no energy is used by the electrons to migrate to the surface, and thus, these electrons end up with the maximum possible kinetic energy, Kmax.
    [Show full text]
  • SOLAR CELLS from Light to Electricity
    SOLAR CELLS From light to electricity This guide provides as accurate an explanation as possible of the complex phenomena behind the transformation of light into electricity. It also includes exercises on energy and light. In addition, at the end of this guide is an experiment that demonstrates the effect of light on the generation of electricity in a photobattery. The experiment is delicate and takes at least one week to work, but it is a good illustration of the impact of light on electric current and is simple to carry out. Please note that the “BATTERY” guide presents the means of storing energy produced using solar panels to ensure Solar Impulse’s energy supply at night. That guide includes instructions to build a small battery. Project: EPFL | dgeo | Solar Impulse Writing: Michel Carrara Graphic design: Anne-Sylvie Borter, Repro – EPFL Print Center Project follow-up: Yolande Berga 1/8 Concepts covered Science • Light and energy Physics • Wavelengths and frequencies • Solar cells and semiconductors • Battery voltage Activity duration Theory: 2 periods One period to present light and light energy, and one for photovoltaic panels. Exercises: 2 periods The exercises are appropriate for all levels. Experiment: 4 periods The experiment is only appropriate in the context of a lab session in a science course that takes place over two weeks, as it takes one week for the device to work. This guide is an opportunity to present students the link between light and electricity and to in- troduce some topics from the history of science and technology. HISTORICAL SIDEBAR The history of solar panels is one of a reaction that plays out at the atomic scale.
    [Show full text]