# I What is magnetic force generated by planar spiral coil?

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1. Feb 20, 2017

### starrob

Hello everybody,
I have a planar spiral coil with wire. I want to move a magnet in vertical direction with the magnetic force generated by coil. I want to know how much impulsion to magnet will be occured on vertical direction. I have been searching for the answer but I am a little bit confused. How can I find my answer? which way should I follow?

2. Feb 20, 2017

### Staff: Mentor

It depends on the position and orientation of your magnet, and on the coil parameters of course. In general the magnetic force between two magnets is a very tricky problem, but for some cases there are good approximations.

3. Feb 20, 2017

### litup

One way would be to build it and shove a known current at a known voltage and have a little bar magnet on a scale and it weighs X and then with the coil say 10 mm away from the bar magnet and the right polarity of current to cause an attraction of the little bar magnet and you can see the difference in the weight of the bar magnet, using enough energy to say make the bar magnet weight be X/2 and do the arithmetic and that would be the pull at that distance. Be a nice experiment.

I built a magnet like that once to accelerate a 1/4 inch diameter steel ball up into the air using 110 VAC as input to a full wave rectifier with some capacitance for filtration making a fair DC and powering that through a Variac. I found using full power, the ball bearing shot all the way to the ceiling! I had to reduce the Variac voltage to something like 10 volts AC to get the ball bearing to just go up about 100 mm or 4 inches or so which was the goal.

In my case, the bearing was below the surface of the flat magnet coil about an inch. I had rigged a set of metal contacts to close a circuit in a relay that switched on the DC with the idea the bearing would just pop up and down, I included a plastic tube about 8 inches long to keep the bearing confined inside that and then let it fly away, so it did, up and down. This was for a science demonstration at my kids grade school. About 100 kids attended that and I had a lot of other gadgets made, the idea was to do science with every day household items so I used two paper plates as the 'mold' to wrap the wires in and cut a hole in the middle to allow movement of the ball bearing. The funny part was it turned out the timinig of the up and down was not regular but chaotic, because of the way I fashioned the contactors, using a cut up Dr. Pepper can where the ball bearing completed the circuit and that to the coil of a relay which controlled the DC power to the coil.

The kids called it 'electronic POP CORN:) and it was the hit of the afternoon:)

4. Mar 2, 2017

### starrob

Thanks for replies! Also, I want to ask that is there any good simulation program which is possible to simulating magnetic field and calculating magnetic force between magnet and spiral coil?