Measurement%20of%20the%20Charge%20of%20an%20Electron

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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
• Millikans Oil Drop Experiment

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Transistor Theory

• Ic AeqVb/kT 1

• Ic collector current
• q charge (eV)
• Vb base voltage of the transistor
• K Boltzmans Constant
• (8.617 342 x 10-5 eV K-1)
• T temperature in Kelvins

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Ohms Law

• V I R

• V voltage (eV)
• I current (amps)
• R resistance (ohms)

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Combining the Equations

• Vrc BeqVb/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
Constant Temperature, Varying Voltage

• Voltage was varied using the potentiometer

• 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 value found using method of least
  squares

• Slop value 31.1452 /- 1.03

• Using the equation Vrc BeqVb/kT

• Slope q/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 qVb/k

Fundamental Charge of an Electron
1.7703 e-19 C /- 6.842 e-21 C
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Error

• Voltmeters
• Vc 1/100 V
• Vb 1/1000 V

• Thermometer
• Single Degree Accuracy

• Resistor
• accurate to only 2

• Statistical Limitations
• limited data

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Conclusion
Part I
1.2648 e-19 C /- 4.18 e-21 C
Part II
1.7703 e-19 C /- 6.842 e-21 C
Average
1.3175 e-19C /- 5.511e-21C
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Improvement

• More Accurate Equipment

• More independent sets of data for statistical
  improvement

• Different Transistors

• Attention to detail in circuit construction

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