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1. Plancks Constant and the Photoelectric Effect Lulu Liu
Partner: Pablo Solis
2. What is the Photoelectric Effect? Incident radiation
3. Predictions Classically, wave mechanics: Eradiation ? I ? E02
4. Presentation Outline Predicted relationship between E and ?
Set up and Parameters
Current vs. retarding voltage data
Analysis Two Methods Linear Fit Method
Results and Error
Conclusions and Summary
5. Hypothesis E = h ?
? is frequency
h is Plancks constant
6. The Experiment
7. Photocurrent vs. Retarding Voltage Raw Data (Example)
8. Normalized Current vs. Retarding Voltage Curves for All Wavelengths
9. Linear Fit Method of Cut-off Voltage Determination Motivation:
Using zero-crossings for Vs determination compromised by back currents and non-linear behavior.
Does behave linearly at low and high limits (discounting forward current saturation).
Fit the low and high voltage data to separate linear regressions. Extrapolate intersection point (Vs,I0) baseline current.
Use three points farthest from Vs. Reasonable chi-squared.
10. Results of the Linear Fit Method
11. Error Contributions and Calculations for Linear Fit Method Two linear regressions y = mx + b with uncertainties on m, ?m1 and ?m2, and b, ?b1 and ?b2 contribute to the error in the X-coordinate of their intersection (Vs) as follows:
12. Determination of Plancks Constant Using Results from Both Methods Linear fit method: h = 9.4 10-16 4.8 10-16 eV s
Deviation point method: h = 2.9 10-15 7.7 10-16 eV s
13. Error Sources and Improvements for Future Trials Random error cannot reduce but better characterization
More trials, more independent trials (reset equipment? time between trials?)
14. Conclusions Verification of hypothesis
observed light behave as a particle
confirmed linear relation between E and ?
18. CPD contact potential difference
19. Zero-Intercept Method