5H30.21 - e/m - Electromagnetic Deflection of Free Electron Beam

Code Number:
5H30.21
Demo Title:
e/m - Electromagnetic Deflection of Free Electron Beam
Condition:
Excellent
Principle:
Measure e/m of Electrons
Area of Study:
Electricity & Magnetism
Equipment:
Daedelon E-Beam Unit, Electron Beam Deflection Tube, 12 V DC Power Supply, 5 kV DC Power Supply (2), Helmholtz Coils (2), Keithley Multimeters (2), Large Tube and Coils (2nd Floor), Heathkit Power Supply (2nd Floor), Variac, 6 Volt Transformer, and Amp and Milliamp Meters (2nd Floor).
Procedure:

The Daedelon unit is designed with safeties so that unit is not damaged.  It will go through a 30 second countdown when first switched on to warm up the filament.  Nothing can be done until this countdown is over.  Data on the unit is:  Coil radius = 150mm.  Coil separation = 150mm.  Coil turns = 130.

Assemble the large apparatus as shown and according to the diagrams enclosed.  The multimeters shown are used if you are going to try to make a measurement and calculation in the classroom.  Trying this before class for practice is a very good idea.  The large setup shown is the one that was used in the labs upstairs.  This is a good one to use in certain cases as you can get the beam to bend full circle.  Be sure to keep the current under 4 amps so as not to burn up the filament.

NOTE: The switch on the Heathkit power supply should be toward the right or B+ output side.  The B+ output knob should be turned up about 1/2 way.  Turn up the variac slowly.  You will not see any movement of the milliamp meter until you reach 3.5 to 4 amps at which time it will move rapidly with small changes of the variac.  A 4.5 amp fuse in the filament circuit would be a good idea when this is used in the classroom.

With the large tube and coils system the Heathkit power supply and some of the meters may be replaced with the current control power supply found in room 250.  The procedure to setting the supply to work with this system is to short the power supply (+ and - terminals) and then apply a little voltage.  Turn the amps up to 4.5 and turn off.  Unplug everything and the power supply should be set to self limit at 4.5 amps.

The electron tube for the large apparatus can still be had from Sargent-Welch.  Item # WL0623.  They usually have them in stock but run a new batch about every year.

References:
  • Eugene Edward Nalence, "Additional Experiments with the e/m Apparatus", TPT, Vol. 60, #9, Dec. 2022, p. 752.
  • Colin S. Wallace, Edward E. Prather, Seth D. Hornstein, Jack O. Burns, Wayne M. Schlingman, and Timothy G. Chambers, "A New Lecture-Tutorial for Teaching about Molecular Excitations and Synchrotron Radiation", TPT, Vol. 54, #1, Jan. 2016, p. 40.
  • Jeremy Brown, "Blending Old Technology With New: Measuring the Mass of the Electron", TPT, Vol. 44, #7, Oct. 2006, p. 457.
  • Larry O. Lamm, "Velocity of q?", TPT, Vol. 31, #2, Feb. 1993, p. 68.
  • A. K. T. Assis and F. M. Peixoto, "On the Velocity in the Lorenz Force Law", TPT, Vol. 30, #8, Nov. 1992, p. 480.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 8", TPT, Vol. 23, #5, May. 1985, p. 277.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 7", TPT, Vol. 22, #8, Nov. 1984, p. 509.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 6", TPT, Vol. 22, #7, Oct. 1984, p. 437.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 5", TPT, Vol. 22, #6, Sept. 1984, p. 368.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 4", TPT, Vol. 22, #5, May 1984, p. 288.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 3", TPT, Vol. 22, #4, Apr. 1984, p. 242.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 2", TPT, Vol. 22, #3, Mar. 1984, p. 150.
  • John le P. Webb, "The Fine-beam Cathode-ray Tube and the Observant and Enquiring Student Part 1", TPT, Vol. 22, # 2, Feb. 1984, p. 80.
  • Richard Gagnon, "Magnetic Mirror: A Visual Demonstration", TPT, Vol. 17, #8, Nov. 1979, p. 529.
  • Paul J. Angiolillo, "On Thermionic Emission and the Use of Vacuum Tubes in the Advanced Physics Laboratory", AJP, Vol. 77, #12, Dec. 2009, p. 1102.
  • Patrick Polley, "Comment on 'On Thermionic Emission and the Use of Vacuum Tubes in the Advanced Physics Laboratory'", AJP, Vol. 78, #8, Aug. 2010, p. 878.
  • Joseph E. Price, "Electron Trajectory in an e/m Experiment", AJP, Vol. 55, #1, Jan. 1987, p. 18.
  • F. C. Peterson, "Instrumenting an e/m Experiment for Use in Large Enrollment Courses", AJP, Vol. 51, #4, Apr. 1983, p. 320.
  • James M. Reynolds, "An e/m Experiment Employing the Magnetic Field of a Flat Circular Coil", AJP, Vol. 40, #2, Feb. 1972, p. 347.
  • George W. Ficken, Jr., Further Modification of e/m Experiment", AJP, Vol. 35, #10, Oct. 1967, p. 968. 
  • Mario Iona, H. Charles Westdal, and P. Roger Williamson, "Modification of e/m Experiment", AJP, Vol. 35, #2, Feb. 1967, p. 157.
  • Peter J. Mohr and Barry N. Taylor, "Adjusting the Values of the Fundamental Constants", Physics Today, Vol. 54, #3, Mar. 2001, p. 29.
  • Freier and Anderson, "Ei-18. Forces on an Electron Beam", A Demonstration Handbook for Physics.
  • David Kutliroff, "99, Measuring the Mass of the Electron", 101 Classroom Demonstrations and Experiment For Teaching Physics, p. 217.
  • Yaakov Kraftmakher, "6.1, Electron", Experiments and Demonstrations in Physics, ISBN 981-256-602-3, p. 361.
  • W. Bolton, "5. Charge-Mass Ratio for Electrons (3)", Book - 3. Atomic Physics, Physics Experiments and Projects, p. 16 - 19.
  • W. Bolton, "4. Charge-Mass Ratio for Electrons (2)", Book - 3. Atomic Physics, Physics Experiments and Projects, p. 12 - 15.
  • W. Bolton, "3. Charge-Mass Ratio for Electrons (1)", Book - 3. Atomic Physics, Physics Experiments and Projects, p. 9 - 11.




Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.