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Measurement of the Charge of an Electron Presented by John Cole Experiment Conducted by John Cole, Sarmadi Almecki, and Pirouz Shamszad
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Abstract
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Theory Fundamental Charge Townsend Millikan’s Oil Drop Experiment
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Transistor Theory I c = A[e qV b /kT –1]I c = collector current q = charge (eV) V b = base voltage of the transistor K = Boltzman’s Constant (8.617 342 x 10 -5 eV K -1 ) T = temperature in Kelvins
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Ohm’s Law V = I RV = voltage (eV) I = current (amps) R = resistance (ohms)
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Combining the Equations V rc = Be qV b /kT Approximates for the specific voltage greater than 1/40 V
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Experimental Setup NPN transistor 2N3904 2 10 turn potentiometer Voltage source Voltmeter (base) Voltmeter (rc) Resistors
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Experimental Setup Temperature was varied in the second part using a heat pump & refrigeration device. Transistor leads were extended so that it could be remotely placed in the temperature controlling device. Mercury thermometer monitored temperature
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Procedure Part I Voltage was varied using the potentiometer Constant Temperature, Varying Voltage Data was recorded at 294.15K
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Procedure Part II Constant Voltage, Varying Temperature Temperature was adjusted via heat pump / refrigerator Data was recorded T
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Part I: Varying Potential Log Scale Logarithmic Scale plotted using gnuplot software
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Part I: Non Log Scale
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Interpretation: Part I Slope = q/kt Slope value found using method of least squares Slop value = 31.1452 +/- 1.03 Using the equation V rc = Be qV b /kT k and t are constants, solved for q Fundamental Charge of an Electron 1.2648 e-19 C +/- 4.18 e-21 C
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Part II: Log Scale
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Part II: Non Log Scale
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Interpretation: Part II Slope found using method of least squares Value of 6411.11 +/- 247.8 slope = qV b /k Fundamental Charge of an Electron1.7703 e-19 C +/- 6.842 e-21 C
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Error Voltmeters »Vc = 1/100 V »Vb = 1/1000 V Statistical Limitations limited data Thermometer Single Degree Accuracy Resistor }} accurate to only 2%
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Conclusion 1.7703 e-19 C +/- 6.842 e-21 C 1.2648 e-19 C +/- 4.18 e-21 C Part I : Part II: Average 1.3175 e-19C +/- 5.511e-21C
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Improvement More Accurate Equipment More independent sets of data for statistical improvement Attention to detail in circuit construction Different Transistors
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