# Physics307L F08:People/Gibson/Plank's Constant Lab Summary

## Idea

The idea behind this lab was to determine the stopping potential of various line spectra from a Hg lamp. The equipment used were as follows: Voltmeter, Hg lamp and difractor, and h/e apparatus. The plan was to hook up the voltmeter to the h/e apparatus to determine how many volts was required to keep the electrons from completing the photoelectric effect (in the h/e apparatus). Each of these were measured for the various line spectra (uv, v, b, g, y ,r) and recorded.

## Analysis

After we were finished recording we used a least squares analysis to determine what h (plank's constant) and Wo (Work function) were. Those results can be seen in the lab manual here: F08:People/Gibson/Notebook/070910 Plank's Constant. After we found our mean value of h, we then proceeded to find the standard deviation and report our value which we (Matt Gooden and I) were quite pleased to show was:

       h=6.87219*10^-34 J*s +/- .3907*10^-34.


This is ridiculously close to the standard value of h we found in most text books to be:

       h=6.63E-34 J*s


NOTE: Alas we realized a little bit too late that to get a better approximation of our ${\displaystyle \sigma }$ we should have divided this by sqrt(N) where N is the number of elements in the data set. For future labs this will be taken into account.