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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


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