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#15443 - 04/28/03 07:32 PM Will magnetized items hurt compasses?

Hey Everybody,
I bought a small compass to add to my keychain, which already has a Photon, mini bic lighter and a SwissTech Utilikey on it. I went to put the compass on and noticed the needle jumping around. On further inspection, the Phillips tip on the Utilikey is magnetized and that's what was causing it, but only at a range of 1 inch or so. Would this ruin a compass if I decided to put it on there? I realize I'd have to remove it to get an accurate reading... Should I maybe ditch the Utilikey or just find another place for the compass? A keychain is a lousy place for a compass, but pretty convenient for me. What do you think?

#15444 - 04/28/03 08:29 PM Re: Will magnetized items hurt compasses?

I would think that it could. If the screwdriver magnet is more powerful it could negatively affect the compass needle. Then again, the fact that the needle swings freely may prevent any problems as it could go with the magnetic "flow".

Probably the safe bet is to keep them separated.


#15445 - 04/28/03 09:22 PM Re: Will magnetized items hurt compasses?
aardwolfe Offline
Old Hand

Registered: 08/22/01
Posts: 923
Loc: St. John's, Newfoundland
Personally, I very much doubt it. I'm not a physicist, but a compass needle is simply a magnet that is freely suspended (in two dimensions). It will point to the strongest magnetic field in the vicinity. If anything, this should strengthen the compass, not weaken it.

One possible exception would be if the compass needle were placed perpendicular to a strong magnetic field for a long period of time.

I did a google search on 'degaussing' and 'compass' and came up with this web site, which (among other things) describes how to degauss an object that has become magnetized:

How does it demagnetize?

Alternating current from the power supply sets up a magnetic field in the degausser that reverses itself sixty times a second. This causes a magnetic field in the object you are trying to demagnetize that also reverses sixty times a second.

To reverse the magnetic field, the field must pass through a point of zero magnetism sixty times a second. Now the magnetic domains don't like changing direction so fast so they act differently during the positive cycle than during the negative cycle; this is called hysteresis.

By decaying the field the hysteresis curve becomes smaller and smaller (less magnetism). Eventually, the magnetic domains orientation becomes random. The magnetic fields are always present in any object. It's just that you mixed up all the magnetic domains so that they have random directions and all their little fields cancel.

I have no idea offhand whether this person is talking through his hat or not. (But I do know of cases where VHS tapes were degaussed by people leaving them on top of the VCR while other movies were playing. I'm pretty sure the alternating current/fluctuating magnetic fields generated by the VCR were the key to this. And AFAIK, it only happens to tapes that are left there for extended periods.)

If you want to carry a compass and a magnetized tool in the same pocket, I think an alternative solution would be to clip the two of them together, so that the compass needle is semi-permanently lined up with the magnetic field. If this isn't an option, then I suppose it would be better off separating them. But I think the chance of your compass being destroyed in this fashion is very low.
"The mind is not a vessel to be filled but a fire to be kindled."

#15446 - 04/28/03 09:51 PM Re: Will magnetized items hurt compasses?
David Offline

Registered: 10/09/02
Posts: 245
Loc: Tennessee (middle)
Probably not...though I once reversed the polarity on my old Boy Scout Explorer Silva Compass.

I was playing around with a magnet & the compass, & "stripped" the compass down the magnet, as if I were trying to magnetize a screwdriver shaft. It worked, somewhat to my chagrin. I repeated the manuver after a couple of minutes, reversing the polarity again--thereby restoring it to normal function--lest I forget what I'd done & tried to use the thing in that state.

Learned an important lesson...& had some fun, too. :-)


#15447 - 04/29/03 01:39 AM Re: Will magnetized items hurt compasses?
johnbaker Offline
old hand

Registered: 01/17/02
Posts: 384
Loc: USA
I don't know about the influence from the magnetism of the screw driver, but I do doubt whether you will be able to get accurate compass readings in proximity to steel tools. Generally I have found that my various steel tools tend to bias my compass readings when they are within 6" or so of the compass. Keeping the compass farther away from the tools is probably better. You might want to relocate your compass, or at least attach it to the key ring with a detachable connection.

Good luck,


#15448 - 04/29/03 08:33 PM Re: Will magnetized items hurt compasses?
WOFT Offline

Registered: 05/10/02
Posts: 391
Loc: Cape Town, South Africa
This might be a long shot, but won't the keys and other things in your pocket damage the compass more due to consistent rough movement? One way to de-magnetise a magnent is to "hit it with a hammer, therby disrupting the alignment of the magnetised particles". I got that from an old science text book (1978 sylabus!!)
'n Boer maak 'n plan

#15449 - 04/29/03 09:23 PM Re: Will magnetized items hurt compasses?

OK, you've gotten some really good posts about how magnets work in theory. I'll try not to reproduce that here so no one gets bored, but I thought a little clarification was necessary.

Other (external) magnetic fields can degauss a magnet if they are varied either with electric currents (such as with an electric degausser) or through motion (where you take a stronger magnet and move it over the weaker one repeatedly). Magnets that can float freely (e.g. a compass needle) as they jangle around in your pocket can orient themselves with the external magnet and will most likely not have their domains realigned.

Physical force can destroy a permanent magnet. For example, beating a magnet with a hammer will send shock waves through the metal that will cause the domains to realign. Physically bending a magnet back and forth in several places can have the same effect. Heating a magnet can demagnetize it as well, in this case the thermal energy is sufficient to randomize the domains as the individual atoms start vibrating faster... we're talking a few hundred degrees or more here.

The short answer to your question is that none of the jostling or the presence of other weak magnets are probably going to be enough to hurt your compass.

Trying to take a reading in the proximity of all that other metal is a different issue, be careful about that. The safest thing would be to detach your compass from the keyring before trying to take reading with it.

Hope this helps.

#15450 - 04/30/03 12:54 PM Re: Will magnetized items hurt compasses?

I can second the motion about getting the compass away from other metallic items before attempting to use it. True story - I was in our new Dick's Sporting Goods checking out the camping and outdoor items, and a guy next to me was seeing if one of those small Brunton watchband compasses would fit on his watch. He told me he wanted to be better prepared in case of a terrorist attack. He was mildly put out when I suggested that he might want to put the compass on something other than his metal expansion wristwatch band - "Oh, will that make a difference?" he asked. Sigh ...


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