Class #8: Quantum Mechanics Born Modern Physics (PC300) Class #8: Quantum Mechanics Born

Test Assessment

Photoelectric Effect - + Photoelectrons. V0 - stopping potential Minimum extra KE that allows electrons to escape is the work function

Photoelectric Effect: Intensity -v0 – stopping potential (stops all photoelectrons no matter what the light intensity). For a given light intensity, there is a maximum photocurrent which is reached as voltage increases from –ve to +ve Makes Sense: more photons - more electrons

Photoelectric Effect: Frequency 1902: Lenard - Maximum KE does not depend on intensity Maximum KE of photoelectrons (material dependent) depends only on light frequency. i.e. light of different frequency requires a different retarding potential (-v0) to stop the most energetic photoelectrons Vo depends on frequency but not intensity. Threshold Frequency (Work Function) below which no electrons are released Lenard - nobel prize on cathode rays 1905 Lenard - Nobel Prize

1905: Photoelectric Effect: Solution Classical electromagnetic theory has problems explaining the independence of Kmax and light intensity, the linear dependence of Kmax on light frequency and the instantaneous (10-9s) response of the photocurrent. Einstein - Light composed of irreducible "grains" - quanta (energy packets). 1905 What a year for Einstein http://www.aip.org/history/einstein/chron-1905.htm 1921 Einstein - Nobel Prize

Photoelectric Effect: Work Functions (Kmax) The smaller the work function, the smaller the threshold frequency that light can eject photoelectrons. No photoelectrons are released for frequencies below this threshold frequency. Draw Graph – No photoelectrons is proportional to intensity (I.e. maximum photocurrent is proportional to the light intensity)

Various Work Functions http://www.youtube.com/watch?v=m55kgyApYrY 1923 Millikan - Nobel Prize Why do different metals have different work functions?

Problem Set for Wednesday To answer the first two questions you will first need to do a Simulation. Run the Photoelectric Effect program by following the steps below.   P:\Academic\White\PC301 Modern Physics 2013\Programs\Photoelectric\Photoelectric_en Take data to answer the following question. 1. Using five different wavelengths striking Sodium, calculate the ratio h/e. (Hint, make a graph in Excel of the Stopping Potential vs. frequency. Include this graph, with a trendline, in your homework solution. And remember, that all graphs need labels, a title, and a short caption…) 2. Find the Workfunction for each of the six elements (most of which are metals…including the unknown) used in the simulation. Make a simple chart of your findings. Write a few sentences that clearly describe what procedure you followed and how you arrived at these conclusions.

Sim #4: Photoelectric Effect P-Drive\White\Modern Physics\Programs\Petutor\CTWINX Click on Photo15.ctb then hit OK

Lab 6 – Photoelectric Effect

X Ray Production 1901 Roentgen - Nobel Prize X-rays are produced when the e-'s are suddenly decelerated upon collision with the metal target; these x-rays are commonly called brehmsstrahlung or "braking radiation Accelerated charges give off electromagnetic radiation, and when the energy of the bombarding electrons is high enough, that radiation is in the x-ray region of the electromagnetic spectrum. It is characterized by a continuous distribution of radiation which becomes more intense and shifts toward higher frequencies when the energy of the bombarding electrons is increased. The curves above are from the 1918 data of Ulrey, who bombarded tungsten targets with electrons of four different energies. 1901 Roentgen - Nobel Prize

EM Spectrum: X-Rays (Duane-Hunt Rule) Same min. wav. (max freq) -> E=hf => when an electron gives up all its KE and creates one photon (inverse photoelectric effect). (W-tungsten, Mo-Molybdenum, Cr-Chromium (Duane-Hunt Rule)

Quantum Homework Questions Some Simulation Questions and an Electron Gun question Also… Thornton and Rex! "Yeah, well I got mine first Due Wed normal time

1897 - J.J.Thompson 1906 - Nobel Prize "identified cathode rays as electrons and measured e/m 1906 - Nobel Prize

X Ray Production X-rays are produced when the electrons are suddenly decelerated upon collision with the metal target; these x-rays are commonly called brehmsstrahlung or "braking radiation Accelerated charges give off electromagnetic radiation, and when the energy of the bombarding electrons is high enough, that radiation is in the x-ray region of the electromagnetic spectrum. It is characterized by a continuous distribution of radiation which becomes more intense and shifts toward higher frequencies when the energy of the bombarding electrons is increased. The curves above are from the 1918 data of Ulrey, who bombarded tungsten targets with electrons of four different energies.

Measuring charge/mass (e/m) Electron beam Cathode Ray CRT predecessor to TV etc B field perpendicular to direction of motion of particles make them move in a circular motion. Cathode Ray Tube Derive in lab

Lab ? - e/m setup

1909 - Robert Millikan Precise Measurement of e Oil Drop Experiment