I make a setup (see attached picture).

  • ONE coil (1" diameter x ~120 turns), which is separated with a gap, is mount on two sides. Each side has an iron rod (1" diameter x 6" long) to increase the focus of the magnetic wave.The wire for the core is 14 gauge motor wire (5.9 amp power rating max).
  • Two super strong magnets (1" diameter x 0.5" thick each) are mount at the middle block (plastic) under Duck tape. Each of them is rated ~40 lbs holding force. Each side of the block has one magnet.
  • I use 6 power resistors in series to create 50 ohm resistance. I connect the circuit to wall power 120VAC. Since the impedance of the coil is small, I think I give 2.4 amp @ 60 HZ to the circuit.
  • Everything for holding is by very smooth plastic (Acetal Resin).
  • Before I connect the power, I put the system at rest. The magnet is so strong that, they make the middle piece to go to either one of the iron.

I thought the MIDDLE PIECE would swing to the left and right with 60Hz. However, the system does NOT move at all. Any idea?

Experiment setup

enter image description here


2 Answers 2


60 Hz is rather fast. While the magnetic fields are strong, the mass (and therefore inertia) of the center magnet is probably so large as to keep it from accelerating quick enough to oscillate at 60 Hz. Try using a power supply with a variable AC output, set to 1 Hz. The mass should probably move in this case. If it doesn't, then there is likely a fault in the setup.

  • $\begingroup$ The circuitry is only a coil and resistors. I used a ohmmeter to measure the total resistance. The total resistance is valid. $\endgroup$
    – Marco
    Jun 7, 2014 at 20:09
  • $\begingroup$ sorry - I should have said there is likely a fault in the experimental setup (not sure what it precisely would be though). I'll fix that in my answer. $\endgroup$ Jun 7, 2014 at 20:11
  • $\begingroup$ I have considered the acceleration problem, that why I put the initial position of the middle piece to swing to ONE side. The magnetic force have a 1/distance^2 relation. I would expect to see at least one big move. Isn't it? $\endgroup$
    – Marco
    Jun 7, 2014 at 20:11
  • 1
    $\begingroup$ How powerful is the "super strong" magnet in relation to the electromagnet? It could be that the added force of the electromagnet is too weak to pull the block off of the magnet on the other side. $\endgroup$ Jun 7, 2014 at 20:24
  • $\begingroup$ *This could compound the aforementioned inertia problem. (add to the end of my previous comment) $\endgroup$ Jun 7, 2014 at 20:33

50 ohms total? And the coil resistance is much lower than 50 ohms?

When you apply 120V, the resistors will quickly burn inside. They won't be 50 ohms anymore (need to measure their resistance with a meter.) The resistance becomes high, and the current drops far below 2.4amps.

Resistor power is V^2/R = 120*120/50 = 244 watts, so your twenty-watt resistors may be destroyed within minutes. If they weren't fried instantly, then expect to see smoke. (If resistors remain cold, then there is a broken connection somewhere.)

Perhaps instead of fragile resistors, instead use two 100watt incandescent light bulbs hooked together in parallel, to give 200w/120v = 1.67amp. That, or use a 1200watt electric heater, for 1200/120 = 10amps.

To produce strong magnetic fields, we usually use 120V and thousands of turns of thinner wire (several KG of copper.) That, or use low voltage, fewer turns, and current far higher than 2.4 amps. Need an expensive step-down transformer that provides lower volts at 50amps or 100amps, etc.

Also: to remain alive and not dead, it's wise to perform many, many experiments with batteries, not with 120VAC. If you work with 120VAC, be very very afraid. This tends to keep you safe, but it's not a guarantee.


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