lab 10 pdf

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Physics Laboratory II- Atomic Physics 1 Lauren Sturm Partners: Jayme Kerrigan, Brianna Juskalian Introduction to General Physics II – Section 067 4/18/18 Introduction: The purpose of this lab is to find understanding in the way electrons move through magnetic fields, and to learn how this movement can be used to figure out the ratio of electron charge to mass. Students will familiarize themselves with the notion of the photoelectric effect and how it is a demonstration of light in a quantum nature. Students will also familiarize themselves with diffraction and find understanding in the way that it is used in spectroscopy in order to identify elements within a sample. Procedure: Part I. The Mass of The Electron Step 1- Power supply should be connected to the apparatus. High voltage power should be used for accelerating voltage. Step 2- Helmholtz coils should be wired together in series. Field coil should generate points that go in the same direction. Red input for one coil should be connected to the end that is positive of the power supply. The black output should then be connected to the red input of the second coil. Attach black output of the second coil to the negative of the power supply. Step 3- Set Filament voltage to that of 6.3VAC. Set Helmholtz coils to 2.0 Amps DC. And Accelerating voltage to 200 VDC. Step 4- Allow cathode to heat up and then the beam of the electron will be curved by the field from the Helmholtz coils. Be sure that the electron beam is in fact parallel to the Helmholtz coils. Step 5- Note what to the circular path radius when magnetic field is increased. Record. Accelerating potential should be increased and the radius of the circular path should be recorded and observed. Step 6- Accelerating potential should be set to 100V and current should be adjusted to bend the coils to a 5cm radius of the circle. Voltage and current should be recorded and graphed. Step 7- Electron beam radius should be measured. Record values. Step 8- Measurement of radius for 125V, 150V, 175V, and 200V should be repeated. Step 9- Power supply should be turned off. Step 10- Compute magnetic field B that is produced by the pair of coils. Step 11- Compute e/m ratio for each voltage. Step 12- Mass of electron should be computed using e=1.6x10^-19 C.

Physics Laboratory II- Atomic Physics 2 Step 13- Average results and compare. Part II. The Photoelectric Effect Step 1- Apparatus should be set up with the photoelectric apparatus, a light source, and multimeter. Step 2- Photoelectric apparatus should be altered and moved so that the spectrum pattern that is brighter appears on the Photoelectric apparatus reflective surface. Step 3- Focus light onto reflective mask that is white of the photoelectric apparatus. Step 4- Light shield should be rolled out of the way to reveal photodiode mask that is inside apparatus. Step 5- The button that reads “Push to Zero” should be pushed down and the change in voltage should be observed. Once voltage ceases movement, this is the value that should be recorded. In first order, this should be replicated for each color. Step 6- Be sure that only one color of light is falling into the mask opening. Variable transmission filer should then be placed on the mask. For 100%, 80%, 60%, 40%, and 20% the voltage should be recorded for the light passing through each. Step 6- Replicate using second color. Step 7- Analyze data. Step 8- Create graph of stopping voltage versus frequency. Part III. Atomic Spectrum of Hydrogen Step 1- So you are able to see through the grading and are able to read meterstick lines, place the grading and meter stick accordingly. Step 2- The distance between grading and meter stick should be recorded. Step 3- Measure meterstick position for each first order color of light. Record values. Step 4- For first order, wavelength of each color should be found. Step 5- Make graph of 1/wavelength versus 1/n^2. Precaution and Sources of Error: There were many sources of possible error within this lab. One source of error, as it happened in my own lab section, was that equipment was not working. In Part I, Part II, and Part III, there were things that went wrong within the lab and all students had to share data with each other to get all the data needed for the analysis of this lab report. In part III, the hydrogen discharge lamp would not turn on and we had to get data from other students. In part I, the room was not dark enough to see the electron beams. As stated, we had to get data from other groups as well as out teacher in order to get accurate data for the analysis of this lab.

Physics Laboratory II- Atomic Physics 3 Data and Calculations: Part I. Accelerating voltage (V) Current (A) Radius- left (m) Radius- right (m) Average radius (m) Magnetic field (T) (e/m) x10 11 (C/kg) m x10 -31 (kg) 100 0.00038 2.95 2.95 2.95 2.9*10^-7 1.32 0.121 125 0.0057 3 3 3 4.4*10^-6 1.36 0.118 150 0.0074 3.25 3.25 3.25 5.7*10^-6 1.37 0.117 175 0.0094 3.75 3.75 3.75 7.3*10^-6 1.36 0.118 200 0.0114 4 4 4 8.8*10^-6 1.35 0.119 Part II. First order color Wavelength (nm) Frequency (10 14 Hz) Stopping potential (V) ultraviolet 365.383 8.20264 1.39 violet 404.656 7.40858 1.52 blue 435.835 6.8785 1.34 green 546.074 5.48996 0.83 yellow 576.960 5.18672 0.80

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Physics Laboratory II- Atomic Physics 4 Color % transmission Stopping potential (V) 1 100 0.80 1 80 0.81 1 60 0.80 1 40 0.82 1 20 0.84 2 100 1.08 2 80 0.83 2 60 0.84 2 40 0.82 2 20 0.83 *1-yellow *2-green Part III. Color of line n= s (cm) x (cm) sin( θ ) Wavelengths (nm) red 3 36 16 0.406 650 blue-green 4 36 11.5 0.304 486 blue-violet 5 36 10 0.267 427

Physics Laboratory II- Atomic Physics 5 Slope: 2.0*10^7 m^-1 Accepted slope value (Rydberg Constant): 1.097 *10^7 m^-1 Percent Difference: 8.23% Questions: Question 1. What happen to the radius of the circular path when you increase the magnetic field strength but keep the accelerating potential fixed? Magnetic field and radius can be found to have an inverse relationship, we know this from the e/m equation. If accelerating potential is fixed, as one increases the other must decrease. Circular path radius would decrease if magnetic field strength was increased. Question 2. What effect does the accelerating potential have on the radius of the circular path? Radius of the circular path would increase with accelerating voltage increase. We can see a direct relationship there. Question 3. How does the stopping potential change with the different color of light? The stopping potential will decrease while moving from a small wavelength of color to a large wavelength. We see an inverse relationship. Question 4. Do the results of the wavelength experiment support a wave or a quantum model of light? Explain. Yes, the results of the wavelength experiment support wave and quantum model of light. High frequency, therefore smaller wavelength, was shown to have greater stopping potential and this greater photoelectron energy. Question 5. What effect does reducing the amount of light have on the stopping potential?

Physics Laboratory II- Atomic Physics 6 An increase in stopping potential will be caused by amount of light being reduced as well as the percent transmission. Question 6. Do the results from this transmission experiment support a wave or a quantum model of light? Defend your answer using your results. A decrease in percent transmission meaning the greater the stopping potential would mean the brighter the light was. So therefore yes, the kinetic energy at its maximum which was proportional to the stopping potential was in fact dependent light intensity Results and Discussion: The purpose of this lab was to find understanding in the way electrons move through magnetic fields, students learned how this movement can be used to figure out the ratio of electron charge to mass. Students familiarized themselves with the photoelectric effect and saw how it was used to demonstrate light in a quantum nature. Students also familiarized themselves with diffraction and found understanding in the way that it was used in spectroscopy in order to identify elements within a sample.

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