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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography


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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 Electric Fields And Potential
 Current and Resistance
 Electromotive Force And Current
 DC Circuits
 Magnetic Materials
 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

Power Loss in Transmission Lines


To Illustrate how power loss in transmission lines decreases with voltage and the effects of this on transmission line design.


The setup consists of two 12V 80W bulbs, three transformers which can step up or down between 12V and 120V and two sets of long connecting wires as shown below.

One suggested procedure is as follows:
  • Connect the nearest light bulb to the 12V output on the transformer connected to the line voltage as shown below. The bulb will light brightly.

  • Now connect the heavy wires between the 12V output and the far bulb.

  • This works well, but running thick wire all over the country would be prohibitively expensive so try to do the same thing with the thin wires.

  • Since the resistance of the thin wires is greater than that of the thick wires, more power is lost in the transmission and the bulb is dimly lit. Now, ideally we want to deliver approx 6.5A at 12V (80W) to the bulb while loosing as little power in the line as we can. Since the resistance of the line is fixed, our only hope is to reduce the current we need to push through the line and therefore reduce the power lost in the line. If we step up the voltage to 120V during the transmission, we only have to send .65A through the transmission line and then step back down to ~12V with enough current to light the bulb brightly.