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Al Tobias (wat4y) - Office: Rm. 201, (434) 924-0538 - Lab: Rm. 202, (434) 924-6800


Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography

PLEASE REQUEST DEMOS MINIMUM 1-WEEK IN ADVANCE

Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.


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 Electrostatics
 Electric Fields And Potential
 Capacitance
 Current and Resistance
 Electromotive Force And Current
 DC Circuits
 Magnetic Materials
 Magnetism
 Inductance
 Induction
 Complex Circuits
 Semiconductors And Tubes
 Transmission Lines and Antennas
 Power Loss in Transmission Lines
 Flash Light Radio
 Fiber Optics Coupled Audio Device
 Lecher Lines
  video  - Microwave Oven Experiments
  video  - Electromagnetic Radiation
 FM Radio
 Spark Gap Tesla Coil

Lecher Lines

Purpose:

To demonstrate a standing electromagnetic wave.

Procedure:

centered image


  DEMO VIDEO DOWNLOAD - HD - 1920x1080 / 27.4Mbps - 647MB size  


  DEMO VIDEO DOWNLOAD - LD - 854x480 / 5.69Mbps - 167MB size  


Using our vacuum tube based CENCO 83 MHz RF oscillator, a standing radio wave (λ = 3.6m) is set up in two parallel copper wires 5.5 m long and 2.5 cm apart. To measure magnetic field intensity, a tuned RLC circuit apparatus, with filament bulb in it, is used to sense magnetic field produced by changing current in the transmission line. To measure E-field, a fluorescent tube is used to sense voltage difference between the parallel wires. Moving the probes along the lines, nodes and anti-nodes of the B and E fields can be found.

CENCO Catalog describing a "Short Wave Demonstration Outfit".

Leybold Note on Lecher Lines.

ie. In the open circuit case (the ends of the copper wires are unconnected), the end must be an E-field anti-node and B-field node). In the animation below, the top case is open circuit, the bottom case is closed circuit:

black dots = current
red arrows = voltage


Hints:

Caution: Don't touch the wires.

Please, have the equipment ON only during the demonstration. Turn the oscillator OFF immediately after you finish with the demo.