5J10.30 - Arcing of an Inductive Circuit

Code Number:
Demo Title:
Arcing of an Inductive Circuit
Energy Dissipation of a Broken Inductive Circuit
Area of Study:
Electricity & Magnetism
0 to 150 volt DC Power Supply, Knife Switch with Long Plexiglas Handle, and Large Inductor.

The power supply, inductor and switch are connected in series. Turn the power supply to 100 to 130 volts. Close the switch for about 5 seconds to allow the magnetic field to build in the coil. Open the switch and observe the large arc that can be created as the magnetic field is dissipated.

Also see 5J20.20 for the demonstrations that show the EMF "kick back" through a light bulb.

A subtle comparison can be made between an inductor and a capacitor using a hand crank DC generator.  When connected to the capacitor, the generator is hard to crank at first and gets easier to crank as you continue.  When you quit cranking the generator will keep going on its own in the same direction as you cranked it.   Do the same with an inductor and it gets harder to crank as you continue and when you let go, it stops and turns in the opposite direction you originally cranked it.

The arc also transmits in the RF.  If you take the hand crank radio and set it at 700 to 750 on the AM band you can hear the RF noise the arc generates.

  • Werner Rieder, "Circuit Breakers", Scientific American, Vol. 224, #1, Jan. 1971, p. 76.
  • Forrest M. Mims III, "Basic Radio Transmitters", Vol. II - Science and Communication Circuits & Projects, p. 132.

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