Planck’s Constant
Data Analysis
- Show a plot of your current Vs. retarding voltage data for one wavelength of light with the iris mostly open and with the iris mostly closed. How much does the amplitude of the signal change by?
- For one iris setting, by eye, estimate the retarding voltage at which the current from the cathode begins to grow exponentially for each wavelength of light that you used. Summarize these results in a plot of retarding potential-at-onset Vs frequency.
- Fit your data from the previous step using a straight line, the slope of which should be
. Determine 
using the CODATA value for the elementary charge: 1.602176634×10−19 C. - Repeat those steps for the other iris setting.
- Compare your value to the CODATA value for h