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1. Planck’s 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 Planck’s 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 Planck’s 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