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Visitors of two public exhibitions A and B are equipped with compasses.

Exhibition A:

I want to guide these visitors along a certain path throughout the exhibition by "overriding" the earth magnetic field so that they can follow there compasses "north" along the path. The path where this deviation should work on is no wider than 1.5 meters. This deviation can be turned on and off by a switch (thus can not be accomplished by permanent magnets).

Exhibition B:

I want to notify the visitors of events by generating a short magnetic pulse that will shortly deviate their compasses. This should work over a ground circle area of at least 1 meter radius.


  • Local earth magnetic field strength is below 65 uT.
  • There are no other electromagnetic influences.
  • Height of compasses above ground are 2 meters maximum.

Research so far:

I built a small solenoid magnet with about 400 windings, 4.8V and iron core. Although getting up to 1400 uT at the magnet itself, it rapidly drops in the distance (between ~1/r^2 and ~1/r^3) to a level where it cannot be distinguished from the earth magnetic field; reaching 70uT as soon as 20cm.

In order to reach compasses in 2 meters height (200cm distance, 20cm*10) I would have to amplify the strength by a factor of 1000 (10^3, because of 1/r^3) in case I assume a Dipole (Wikipedia). I doubt this can be accomplished with my small self-built magnet.

What would be the most cost- and time-efficient way to accomplish exhibition A and B?

In particular I'm interested in:

  • how to simulate such an environment on a computer,
  • what kind of magnet type/layout is suitable,
  • can this be accomplished with off-the-shelf equipment,
  • are there any dangers for the visitors.

I'm happy to provide more details if needed.

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closed as off topic by David Z Apr 12 '12 at 17:29

Questions on Physics Stack Exchange are expected to relate to physics within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here.If this question can be reworded to fit the rules in the help center, please edit the question.

Hi InteractiveCube, and welcome to Physics Stack Exchange! This is a site for conceptual questions about physics, not really about how to build devices. So asking about the most cost- and time-efficient way to accomplish something, or whether it can be done with off-the-shelf components, or whether it poses a danger to humans, is not on topic for this site. However, if you edit your question to focus on the physical principles involved, I'll be happy to reopen it. – David Z Apr 12 '12 at 17:29