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diff --git a/pe-effect.tex b/pe-effect.tex index e402a41..963af5e 100644 --- a/pe-effect.tex +++ b/pe-effect.tex @@ -10,7 +10,7 @@ \section*{History} - The photoelectric effect and its understanding was an important step in development + The photoelectric effect and its understanding was an important step in the development of quantum mechanics. You probably know that Max Planck was the first to postulate that light was made up of discrete packages of energy. At that time it was a proposed hypothetical light property that allowed for the proper description of black body radiation. Several years after Planck made this @@ -69,7 +69,7 @@ all those electrons come from? From the photoelectric effect, of course! A laser beam is aimed at a cathode consisting of a material like copper or GaAs. The frequency of the laser is such that electrons will be emitted from the cathode. In this way, high current electron beams are produced. One benefit of -using a laser and the photoelectric effect is that if the laser is "pulsed" in +using a laser and the photoelectric effect is that if the laser is ``pulsed'' in time, the electron beam will be also (this allows synchronized timing in the experiments). Also, the polarization of the laser can be manipulated to allow for the emission of electrons with particular spin. See: www.jlab.org @@ -92,7 +92,7 @@ lines in both the first and the second diffraction orders on both sides. Keep in Often the first/second order lines on one side are brighter than on the other - check your apparatus and determine what orders you will be using in your experiment. -After that instal the $h/e$ Apparatus and focus the light from the Mercury Vapor Light Source onto the slot in +After that install the $h/e$ Apparatus and focus the light from the Mercury Vapor Light Source onto the slot in the white reflective mask on the $h/e$ Apparatus. Tilt the Light shield of the Apparatus out of the way to reveal the white photodiode mask inside the Apparatus. Slide the Lens/Grating assembly forward and back on its support rods until you achieve the sharpest image of the aperture centered on the hole in the photodiode mask. @@ -113,7 +113,7 @@ the $h/e$ Apparatus. potential on the intensity of light} \begin{enumerate} \item Adjust the $h/e$ Apparatus so that one of the blue first order spectral lines falls upon the opening of the mask of the photodiode. -\item Press the instrument discharge button, release it, and observe how much time\footnote{Use the stopwatch feature of your cell phone? You don't need a precise measurement.} is required to achieve a stable voltage. +\item Press the instrument discharge button, release it, and observe how much time\footnote{Use the stopwatch feature of your cell phone. You don't need a precise measurement.} is required to achieve a stable voltage. \item It's important to check our data early on to make sure we are not off in crazyland. This procedure is technically known as ``sanity @@ -141,8 +141,7 @@ the $h/e$ Apparatus. that the light passes through the section marked 100\% and reaches the photodiode. Record the DVM voltage reading and time to recharge after the discharge button has been pressed and released. -\item Do above measurements for all sections of the variable transmission filter. -released. +\item Do the above measurements for all sections of the variable transmission filter. \end{enumerate} @@ -187,7 +186,7 @@ leaks off. \item Use the table in Fig.~\ref{fig:mercury_spectrum} to find the exact frequencies and wavelengths of the spectral lines you used and plot the measured stopping potential values versus light frequency for of measurements of the first and second order lines (can be on same graph). -\item Fit the plots according to $eV_0 = h\nu-\phi$, extracting values for slopes and intercepts. Find average value for slope and its uncertainty. From the slope, determine $h$ counting $e=1.6\cdot10^{-19}$~C. Do your measured values agree with the accepted value of $h=2\pi\cdot 10^{-34}$J$\cdot$s within experimental uncertainty? +\item Fit the plots according to $eV_0 = h\nu-\phi$, extracting values for slopes and intercepts. Find the average value for slope and its uncertainty. From the slope, determine $h$ counting $e=1.6\cdot10^{-19}$~C. Do your measured values agree with the accepted value of $h=2\pi\cdot 10^{-34}$J$\cdot$s within experimental uncertainty? \item From the intercepts, find the average value and uncertainty of the work function $\phi$. Look up some values of work functions for typical metals. Is it likely that the detector material is a simple metal? |