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diff --git a/pe-effect.tex b/pe-effect.tex index 963af5e..7c733c8 100644 --- a/pe-effect.tex +++ b/pe-effect.tex @@ -78,7 +78,7 @@ for the emission of electrons with particular spin. See: www.jlab.org \section*{Procedure} \textbf{Equipment needed}: Pasco photo-electric apparatus, Hg lamp, digital -voltmeter. The Pasco apparatus contains a circuit which automatically determines the stopping potential, which you measure off of a voltmeter, so there is no need to adjust the stopping potential yourself or measuring the current (lucky you!). Read the brief description of its operation in the appendix. +voltmeter. The Pasco apparatus contains a circuit which automatically determines the stopping potential, which you measure off of a voltmeter, so there is no need to adjust the stopping potential yourself or measure the current (lucky you!). Read the brief description of its operation in the appendix. \begin{figure} \centering \includegraphics[width=\linewidth]{./pdf_figs/pefig3} \caption{\label{pefig3} @@ -194,7 +194,7 @@ Use the table in Fig.~\ref{fig:mercury_spectrum} to find the exact frequencies \section*{Appendix: Operation principle of the stopping potential detector} -The schematics of the apparatus used to measure the stopping potential is shown in Fig.~\ref{pefig5}. Monochromatic light falls on the cathode plate of a vacuum photodiode tube that has a low work function $\phi$. Photoelectrons ejected from the cathode collect on the anode. The photodiode tube and its associated electronics have a small capacitance which becomes charged by the photoelectric current. When the potential on this capacitance reaches the stopping potential of the photoelectrons, the current decreases to zero, and the anode-to-cathode voltage stabilizes. This final voltage between the anode and cathode is therefore the stopping potential of the photoelectrons. +The schematic of the apparatus used to measure the stopping potential is shown in Fig.~\ref{pefig5}. Monochromatic light falls on the cathode plate of a vacuum photodiode tube that has a low work function $\phi$. Photoelectrons ejected from the cathode collect on the anode. The photodiode tube and its associated electronics have a small capacitance which becomes charged by the photoelectric current. When the potential on this capacitance reaches the stopping potential of the photoelectrons, the current decreases to zero, and the anode-to-cathode voltage stabilizes. This final voltage between the anode and cathode is therefore the stopping potential of the photoelectrons. \begin{figure}[h] \centering \includegraphics[width=0.7\linewidth]{./pdf_figs/pe_det} \caption{\label{pefig5} The electronic schematic diagram of the $h/e$ @@ -209,7 +209,7 @@ front panel of the apparatus. This high impedance, unity gain ($V_{out}/V_{in} voltmeter. Due to the ultra high input impedance, once the capacitor has been charged from -the photodiode current it takes a long time to discharge this potential through +the photodiode current, it takes a long time to discharge this potential through some leakage. Therefore a shorting switch labeled ``PUSH TO Zero'' enables the user to quickly bleed off the charge. \newpage |