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Planck s Constant and the Photoelectric Effect

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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 ?
Experimental techniques
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