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Answer all questions completely SHOW YOUR CALCULATIONS - Watch sig fig.

(Three tables and two graphs should be included from Parts A,B, & C. Each must be properly and completely labeled).


1) From equations (1) and (2) derive the linear equation of the graph that you plotted in Part A.


2) Use this new equation and the graphs in Part A to calculate the Planck’s constant h in eV and the work function Φ in eV from the slope and the y intercept of the graph.


3) Using the information on the next page, use LINEST in Excel to calculate errors ∆h and ∆Φ. Label and explain each value in table for LINEST. Give your final result in the following form: For 8 mm aperture: h ± ∆h eV·s, and Φ ± ∆Φ eV


4) Estimate the threshold frequency for this setup.


5) Compare your experimental results for the Planck’s constant with the

accepted value of: h = 6.6261 × 10-34 J s = 4.1357 × 10-15 eV s.

Did the accepted value fall within your uncertainty range? Calculate your percent error. Look at your data set and graph. Does one or more of your data points fall far from the "best fit" line? If so, explain how this could have happened and what your results would be for the value of h if you neglect this errant data point.


6) Refer to Part B and give a brief definition of what saturation current means in terms of photons, current and voltage. Review the graph you created for Part B, and give a rough estimate for the saturation current based on the data.


7) Refer to Part C and explain Theoretically how decreasing the aperture size affects the photoelectric current, that is, as the aperture is from 8 to 4mm, and then from 4 to 2 mm, state the expected change in current? How did your actual results in Part C compare to this?


8) Name four specific sources of error, and state if they are random or systematic errors. Your values of h cannot have the same number of significant figures as the numbers as the accepted value for h given above. Explain why you cannot claim 5 significant figures with this apparatus.

Continued on next page....


9) Look at the two simplified graphs.

Both of them are graphs of photoelectric current's (i) dependence on potential difference (V).

Use them to explain clearly how light intensity and wavelength of the incident light affects the stopping voltage and the saturation current of the photoelectrons.


Incident Light wavelengths
Incident Light Intensities


How to use LINEST in EXCEL   1) Select four cells in EXCEL. They should be near the data table.   2) While they are highlighted type =LINEST( into the function bar You will see the above if you have done this correctly Now do the following in order:   a) Select all the values you wish to use for known y's, then add a comma b) Select all the values you wish to use for known x's, then add a comma c) type 1, then a comma d) type 1 and then add a closed bracket ) e) Hit the keys Ctrl, SHIFT and ENTER at the same time.   3) The four boxes will now have numbers in them. They are
the slope the y intercept
uncertainty in the slope uncertainty in y intercept


4) Be sure that you label each box with what it actually means in this experiment. Therefore, state what the slope is, and what the y intercept is.


5) Be sure to change significant- figures to be appropriate to the data as it was collected.

10) Be sure to include a short conclusion summarizing your results and their meaning.

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