Answer the Activity 2 and the assignment part.

2. Click the lamp to turn on the light. When reading currents, click on the red button each time the brightness or color is changed. Read the texts so that you will be guided properly. Ask your teacher for assistance when necessary. (Note: The animation shown is a representation of the photoelectric effect. The large oval with an opening represents a tube with a window to let light in and two metal plates on either end. When light from the lamp enters the opening and hits the plate on the left, electrons are emitted. They cross the tube and hit the plate at the right end of the tube. A current is then measured by the ammeter. The wave theory of light says that since light is a wave, the energy of the light (wave) depends on the amplitude (or brightness) of the light (wave). The kinetic energy of the resulting electrons called photoelectrons) is equal to the energy of the incoming light minus the amount of energy needed to free the electrons from the atoms of the plate (called the work function). The kinetic energy of the photoelectrons can be experimentally measured by using a battery to make the plate on the right negatively charged. The electrons can still hit the plate if they have enough energy. As the plate is made more and more negative, fewer and fewer electrons have enough energy to hit the plate. Finally, the plate can be made so negative that even the electrons with the most energy are unable to hit the plate and the current in the circuit (measured by the ammeter) goes to zero. The negative voltage that causes the current to go to zero is called the stopping potential). 3. Try each of the experiments given in the simulation and answer the questions on your answer sheet Experiment #1: Change the color in order from blue down to red. Observe and take note what happens. Experiment #2: Set the color to blue and change the brightness. Observe and take note what happens. Experiment #3: Read the definition of stopping potential above. Set the color to blue and the brightness to High. Click the battery button then click each battery setting in order from low voltage to high voltage. Find the voltage that causes the current to go to zero and record it on your answer sheet. Repeat this for each color. Remember to click the red battery button every time you change the light color. Observe and take note what happens. Experiment #4: Do an experiment to answer the following question. Observe and take note what happens. - OF A TT TTAITVER SI . IV. ANALYSIS/OBSERVATION Experiment #1 What effect does changing the color of light have on the ejected photoelectrons? Experiment #2 What effect does changing the brightness of the light have on the photoelectrons? Experiment #3 What effect does changing the color of light have on the stopping potential? Experiment #4 For a given color of light, does changing the brightness change the stopping potential? Generalizations:ASSIGNMENT Direction: Solve the following problems completely and correctly. Photoelectric Effect 1. The work function of Potassium metal is 2.3 eV. a) What is the maximum wavelength of light that is needed to free an electron from the surface of a Potassium metal? b) If light with a wavelength of 425 nm shines on this metal, what will be the kinetic energy of the ejected photoelectron in ev? c) What will be the speed of this photoelectron? Compton Effect 2. A monochromatic x-ray beam whose wavelength is 55.8 pm is scattered through 46. What is the wavelength of the scattered beam?Activity 2 A. Photoelectric Effect Discovery 1. Objective: Trace the history of the discovery of the photoelectric effect. II. Direction: 1. Arrange the jumbled letters (names of physicist) and pictures of physicists in their proper place in Table 2 below that correspond to the discoveries placed in column C 2. Using colored ball pens (one for each person), draw a line to connect each name and picture to their corresponding name and contributions. A. Physicist B. Picture C. Discovery (about Photoelectric Effect 1. LETBRA I was the first to observe the NIESNITE photoelectric effect in 1887 when I performed my experiment on the spark-gap generator. The unit of frequency is named after me. 2. HINCHIER 5 Iam an assistant of the one who ZERTH performed the spark-gap generator experiment. I found out and said in 1902 that the velocity of the electrons ejected by ultraviolet light from a metal plate is entirely independent to the intensity of light. 3. PLIPHIP I explained the photoelectric effect LANDER and I am famous because of my theory of relativity. I won the Nobel Prize in Physics in 1921 because of my explanation. B. Discover Me (Photoelectric Effect) More 1. Objectives. Relate and discuss the relationship between frequency and intensity of the photon of light to the kinetic energy and number of the ejected photoelectrons/photoelectron current. II. Materials Computer Unit or Laptop (with online access or saved interactive simulation on photoelectric effect) Ill. Procedure 1. Log on to the Internet and open this URL: http://www.lpscience.fatcow.com/mgagnon/Photoelectric Effect/photoelectriceffe ct1.htm (Note: If the simulation has been downloaded and saved by the teacher in the computer, the students will just be instructed to open the simulation and then explore it.)Notes that may help you to answer the following questions above: LESSON 1 The Quantum Theory of Light By the end of the 19th century, the battle over the nature of light as a wave or a collection of particles seemed over. James Clerk Maxwell's synthesis of electric, magnetic, and optical phenomena and the discovery by Heinrich Hertz of electromagnetic waves were theoretical and experimental triumphs of the first order. Along with Newtonian Mechanics & Thermodynamics, Maxwell's electromagnetism took its place as a foundational element of Physics. However, just when everything seemed to be settled, a period of revolutionary change was ush ered in at the beg the 20th century. A new interpretation of the em mental methods that opened the atomic world for study led to a radical departure from the classical theories of Newton and Maxwell-QUANTUM MECHANICS was born. Once again, the question of the nature of light was reopened. Quantum theory tells us that both light and matter consists of tiny particles which have wavelike properties associated with them. Light is composed of particles called photons, and matter is composed of particles called electrons, protons, neutrons. It is only when the mass of a particle gets small enough that its wavelike properties show up. To help understand all this let us look at how light behaves as a wave and as a particle. Wave-Particle Duality of Light In Physics and Chemistry, wave-particle duality holds that light and matter exhibit properties of both waves and of particles. A central concept of quantum mechanics, duality addresses the inadequacy of conventional concepts like "particle" and "wave" to meaningfully describe the behavior of quantum objects. The idea of duality is rooted in a debate over the nature of light and matter dating back to the 1600s, when competing theories of light were proposed by Christiaan Huygens and Isaac Newton. Through the work of Albert Einstein, Louis de Broglie and many others, it is now established that all objects have both wave and particle nature (though this phenomenon is only detectable on small scales, such as with atoms), and that a suitable interpretation of quantum mechanics provides the over-arching theory resolving this ostensibly paradox. Publicized early in the debate about whether light was composed of particles or waves, a wave-particle dual nature soon was found to be characteristic of electrons as well. The evidence for the description of light as waves was well established at the turn of the century when the photoelectric effect introduced firm evidence of a particle nature as well. On the other hand, the particle properties of electrons was well documented when the De Broglie hypothesis and t subsequent experiments by Davisson and Germer established the wave nature of the electron. Photoelectric Effect Davisson-Germer Experiment Electrons peak at 5 Showed Showed wave particle properties of properties electrons of light Sodium metal Photocredit: http://hyperphysics.phy-astr.gsu.edu/hbase/mod1. html#c2 >WAVE-LIKE BEHAVIOR OF LIGHT In the 1600s Christiaan Huygens, a Dutch physicist, showed that light behaves like a wave. wave length wave crest e.g. sound waves water waves light waves wave trough One behavior of waves is Diffraction wave fronts Diffraction : spreading out of plane waves as they pass through hole. wall with hole wave wave crest trough Q&A As the width of the slit becomes larger than the wavelength the wave is diffracted less.Another behavior of waves is Interference (\"1\"an twin Ilill-tla-tI-nt .- tx ( tan whirl: won- 1 will mwl A Dennison blurb-Inca can Mullen-n M with I\"! It was James Clerk Maxwell Mio showed In the Loans that light is an electromagnetic wave that travels through space at the speed of light. The frequency of light is related to its wavelength according to speed of light / = 3. '\\ frequency '5' v wavelength Let's look at the sample calculation below. Examplel'roblem: The light blue glow given off by mercury street lamps has a wavelength of A = 436nm. What is its frequency? 9 \"g: 3.00xw'ml i 10 nm ammo"? 1 s 436nm m The unit s" is so common when talking about waves that it was given the name Hertz. That is. 1 s'1 = 1 H1. Thus. we would say that light with a wavelength of 436 nm corresponds toafrequencyofx 101'Hertz. The region from A a: 400-750 nm is visible to the human eye and is therefore called the visible region of the electromagnetic radiation. As we saw in the example above. blue light is near the high frequency limit of our eyes. lied light, with wavelengths near 750 nm are at the low frequency limit of our eyes. Light that contains all frequencies in the visible region will appear as white light. More generally, the different regions of the electromagnetic spectrum are given different names. Below are the names given to the different regions {frequency ranges) of light according to their frequency range. '2 10" to" 10" 10'" 10\" Hz l 10' 10' to\" 10' 10'\" 10 > PARTICLE-LIKE BEHAVICII CF LIGHT At this point you may think that it is obvious that light behaves like a wave. 50, why how do we know that light is really composed of particles called photons? Support for this idea comes from an experiment that is called the photoelectric effect which will be discussed in the succeeding part of this module. To learn more about the Quantum Theory of Light and its Dual Nature, watch these video clips by clicking the given links: QUANTUM MECHANICS EXPLAINED IN UNDER 8 MINUTES By London City Girl (2019) https://www.youtube.com/watch?v=8HkPAE_9Q1Y Quantum Mechanics of the Electron by Professor Dave (2015) https://www.youtube.com/watch?v=t8mMN2X5_Vw LESSON 2 BLACKBODY RADIATION All normal matter at temperatures above absolute zero emits electromagnetic radiation, which represents a conversion of a body's internal thermal energy into electromagnetic energy, and is therefore called thermal radiation. Conversely, all normal matter absorbs electromagnetic radiation to some degree. An object that absorbs ALL radiation falling on it, at all wavelengths, is called a BLACKBODY. When a blackbody is at a uniform temperature, its emission has a characteristic frequency distribution that depends on the temperature. This emission is called blackbody radiation. A room temperature blackbody appears black, as most of the energy it radiates is infra-red and cannot be perceived by the human eye. Because the human eye cannot perceive light waves at lower frequencies, a black body, viewed in the dark at the lowest just faintly visible temperature, subjectively appears grey, even though its objective physical spectrum peaks in the infrared range. When it becomes a little hotter, it appears dull red. As its temperature increases further it becomes yellow, white, and ultimately blue-white. Figure 1: Blackbody Radiation. When heated, all objects emit electromagnetic radiation whose wavelength (and color) depends on the temperature of the object. A relatively low-temperature object, such as a horseshoe forged by a blacksmith, appears red, whereas a higher-temperature object, such as the surface of the sun, appears yellow or white. Images used with permission from Wikipedia. Blackbody radiation has a characteristic, continuous frequency spectrum that experimentally depends only on the body's temperature. In fact, we can be much more precise: A body emits radiation at a given temperature and frequency exactly as well as it absorbs the same radiation. This statement was proved by Gustav Kirchhoff: the essential point is that if we instead suppose a particular body can absorb better than it emits, then in a room full of objects all at the same temperature, it will absorb radiation from the other bodies better than it radiates energy back to them. This means it will get hotter, and the rest of the room will grow colder, contradicting the second law of thermodynamics. Thus, a body must emit radiation exactly as well as it absorbs the same radiation at a given temperature and frequency in order to not violate the second law of thermodynamics. Any body at any temperature above absolute zero will radiate to some extent, the intensity and frequency distribution of the radiation depending on the detailed structure of the body. To begin analyzing heat radiation, we need to be specific about the body doing the radiating: the simplest possible case is an idealized body which is a perfect absorber, and therefore also (from the above argument) a perfect emitter. For you to learn more about Blackbody, open the powerpoint presentation | uploaded as additional resource in our mVLE and/or watch the video clips about it through the links provided for you below: Quantization of Energy Part 1: Blackbody Radiation and the Ultraviolet Catastrophe By Professor Dave (2017) https://www.youtube.com/watch?v=7BXvc9W97iU Blackbody Radiation By UNL Astronomy (2014) https://www.youtube.com/watch?v=_Otkbp8yk-wLESSON 3 PHOTONS: THE QUANTA OF LIGHT According to the Planck hypothesis by Max Plank, all electromagnetic radiation is quantized and occurs in finite "bundles" of energy which we call PHOTONS. The quantum of energy for a photon is not Planck's constant h itself, but the product of h and the frequency (f or u). The above quantization implies that a photon of blue light of given frequency or wavelength will always have the same size quantum of energy. For example, a photon of blue light of wavelength 450 nm will always have 2.76 ev of energy. It occurs in quantized chunks of 2.76 ev, and you can't have half a photon of blue light - it always occurs in precisely the same sized energy chunks. But the frequency available is continuous and has no upper or lower bound, so there is no finite lower limit or upper limit on the possible energy of a photon. On the upper side, there are practical limits because you have limited mechanisms for creating really high energy photons. Low energy photons abound, but when you get below radio frequencies, the photon energies are so tiny compared to room temperature thermal energy that you really never see them as distinct quantized entities - they are swamped in the background. Another way to say it is that in the low frequency limits, things just blend in with the classical treatment of things and a quantum treatment is not necessary. frequency of radiation, sometimes written as f giving expression E = hf. E = hv Quantum energy of a photon. h = Planck's constant = 6.626 x 10 Joule-sec = 4.136 x 10 eV-s Note: Joule (J) is the standard unit of energy (E). Another unit is the electronvolt (ev). The relationship of the two units is given by: 1 ev = 1.6 x 10-19 J Example Problem: How much is the energy (in eV) does an AM radio wave of 106 Hz have? Given: f = 106 Hz or /s; h = 4.136 eV.s; E = ? Solution: E = hf = 4.136 eV.s (106 /s) = 4.136 MeV Answer: An AM radio wave of 106 Hz has an energy equal to 4.136 MeV! Photon Energies for EM Spectrum Television Inrrared Visible light Gamma rays Short wave AM Radio Ultraviolet FM radio Millimeter telemetry Microwaves waves X-rays radar radio 18 1 10 10 10 10 10 10 12 13 14 15 16 17 18 10 10 10 10 10 10 10 10 10 Hz Low frequency High frequency Long wavelength Short wavelength Low quantum energy High quantum energy Photocredit: http://hyperphysics.phy-astr.gsu.edu/hbase/mod2.html#c3 To learn more about photons, watch a video clip by following the link below: Quantization of Energy Part 2: Photons, Electrons, and Wave-Particle Duality By Professor Dave (2017) LESSON 4 tube.com/watch?v=eU6VqGIc-2QLESSON 4 tube.com/watch?v=eU6VqGIc-2Q PHOTOELECTRIC EFFECT Electrons ejected The remarkable aspects of the photoelectric effect when it was Light from the first observed were: shining surface / on clean 2 1. The electrons were emitted sodium immediately - no time lag! 2. Increasing the intensity of metal the light increased the number in a of photoelectrons, but not their vacuum maximum kinetic energy! 3. Red light will not cause the Sodium metal ? ejection of electrons, no matter what the intensity! 4. A weak violet light will eject only a few electrons, but The details of the photoelectric effect were in direct their maximum kinetic contradiction to the expectations of very well ? energies are greater than those developed classical physics. for intense light of longer wavelengths! The explanation marked one of the major steps toward quantum theory. An important feature of this experiment is that the electron is emitted from the metal with a specific kinetic energy (i.e. a specific speed). Now anyone who is familiar with the behavior of waves knows that the energy associated with a wave is related to its amplitude or intensity. For example, at the ocean the bigger the wave, the higher the energy associated with the wave. It's not the small waves that knock you over it's the big waves! So, everyone who thought light is just a wave was really confused when the intensity of the light was increased (brighter light) and the kinetic energy of the emitted electron did not change. What happens is that as you make the light brighter more electrons are emitted but all have the same kinetic energy. Well, they thought the kinetic energy of the emitted electron must depend on something. So they varied the frequency of the light and this changed the kinetic energy of the emitted electron. Ekin Kinetic Energy increases linearly with increasing frequency Kinetic Energy of emitted electron 0 Vo Frequency of light shown on metal However, there is a critical frequency for each metal, Vo, below which no electrons are emitted. This tells us that the kinetic energy is equal to the frequency of the light times a constant (i.e., the slope of the line). That constant is called Planck's Constant and is given the symbol h. h = 6.63 x 10-34 J . s - A, the concluding result can be rewritten as A = Ac (1 - cose) . Where: ) = wavelength of the incident photon A' = wavelength of the scattered electron 0 = angle of scattering of the electron For more information about the Compton Effect, watch a video clip following this link: What is Compton scattering? The evidence for x-rays as particles By PhysicsHigh (2020) https://www.youtube.com/watch?v=cwapZ713PHo Compton Effect or Compton Scattering (Animated Story) By Quahntacy-Animating Universe (2018) https://www.youtube.com/watch?v=meYIlYgHROQ Physics - Modern Physics (9 of 26) Compton Scattering (A Sample Problem Solving By Michel van Biezen (2013) https://www.youtube.com/watch?v=Eetchm5kn1s