Compass flips magnetic polarity

[RyanX]

Today I picked up an old compass I had sitting on my desk buried in a stack of books. To my surprise, the compass points directly south instead of north. Although, I was pretty sure a worldwide pole shift did not occur, I grabbed another compass from the closet just to make sure it was indeed the compass and not the earths magnetic field. Sure enough, the compass that was sitting on my desk did indeed flip its polarity.

I thought I understood magnetism to some degree, but I wasn't aware that magnets could flip polarity outside of being exposed to a pretty large magnetic field? I remember as a kid rubbing large bar magnets on nails to make new magnets out of the nails That process seemed to make sense since one is slowly reorienting the magnetic domains of the iron nail as the magnet passes over it. I know that certain magnets can slowly lose their magnetism over time and this is usually dependent on the material of the magnet.

As far as I could tell, this compass was sitting unmolested on my desk fairly well protected by the stack of books surrounding it. The only thing I could think of that could possibly effect its magnetism is my laptop which for half the week sits on the desk in use. I don't understand how any workings of the laptop could effect the compass needle though. I used the second compass to test for any large magnetic fields surrounding the laptop and so far have found none. I'm sure there is a perfectly reasonable explanation for this polarity flip, but so far it has eluded me. Even if this flip was due to an external magnetic field of some sort, what are the chances that the domains would line up to point exactly south? I'm baffled.

Ryan

 

[bedower]

RyanX, this is probably a dumb suggestion, but did you check that the 'flipped' needle wasn't just stuck? This used to happen with a compass I had a few years ago. A sharp tap on its side usually sorted it out.

:)

 

[RyanX]

RyanX, this is probably a dumb suggestion, but did you check that the 'flipped' needle wasn't just stuck? This used to happen with a compass I had a few years ago. A sharp tap on its side usually sorted it out.

:)

Haha! I know, that's what I thought too when I first looked at it, but the needle is freely moving. I can even make another picture with the needle pointing in another direction to verify. After moving it around awhile, I realized it actually would just keep realigning itself to south.

I'm 100% positive that it wasn't like this before since I've used this compass (the one pointing south) on many a hike through the woods. We even used it last fall in a school lesson with the girls, and I'm positive that it pointed north at that time.

I'm just wondering if this is something that has been observed happening with other compasses and/or magnets. Surely I can't be the first to notice something like this.

Either that or this is a really good practical joke! I suppose somebody could have secretly replaced the needle.

 

[Buddy]

Since the compass in question appears to be one of the 'less expensive types', it probably doesn't have precision and reliability built-in. Since the polarity has 'flipped', my guess is that the needle has become magnetized.

My 2 cents? Do the following excercise and throw away the mis-matched compass without another thought.

[quote author=_http://www.uen.org/Lessonplan/preview.cgi?LPid=2703]

Make a compass out of a needle. Rub a needle with a magnet. Make sure you always rub it in the same direction. The needle becomes magnetized. By placing the needle on a cork floating on water, one end will point toward the North pole and the other end will point toward the South pole. A compass has been made. The end pointing toward the North pole is called the north end of the compass and the end pointing toward the South pole is called the south end of a compass. The ends are, therefore, named North (N) and South (S) because of the direction each points.
[/quote]


Some possibly useful info:

[quote author=_http://gorp.away.com/gorp/publishers/menasha/how_navi.htm]
A compass of lesser quality may have a north-seeking arrow that jams against the inside of the bezel ring when it is not perfectly level. Avoid this problem by not buying a cheap compass. And if your compass has a slope scale, do not confuse it with the bezel ring's degree scale. A slope scale is a feature that allows you to judge the degree of slope of a distant hillside or mountainside.
[/quote]

 

[bedower]

A compass of lesser quality may have a north-seeking arrow that jams against the inside of the bezel ring when it is not perfectly level.

Phew! Not totally dumb, then! That is a relief! Thanks, Buddy. ;)

Ryan, perhaps if you took it outside again away from anything electrical, and it realigns itself, then you will know that it was something on your desk that was putting it out of kilter. Your laptop as the culprit springs immediately to mind.

 

[RyanX]

Ok, I think I understand what might be happening here:

_http://www.coolmagnetman.com/magstren.htm

Experiment

1. Obtain samples of ceramic magnets, alnico magnets and a NdFeB magnet. Mark the North pole on each magnet (use a compass to determine which is the N end of each magnet. Remember, the South end of the compass will point to the North pole of your magnet).

2. Measure the strength of the flux using the same method suggested above for measuring temperature affects. Write down your observations. Then check the polarity of the magnet using your compass. Write down your observations.

3. Take the NdFeB magnet and place it against the ceramic magnet, North pole against North pole. Leave it there for a day. Tape or rubber-band the magnets together to keep them in that position. Do the same thing with the alnico magnet and the NdFeB magnet the next day.

4. Measure the strength of the flux for each magnet again and note the difference. Also check its polarity. Write down your observations.

5. Now, take the NdFeB magnet and place its South pole against the marked North pole of the ceramic magnet. Leave it there for a day. Do the same thing with the alnico magnet and the NdFeB magnet the next day.

6. Again, measure the strength of the flux for each magnet and note the difference. Also check its polarity. Write down your observations.

7. You should see that the flux measurement for the NdFeB magnet does not change. However, the ceramic and alnico will change greatly. The poles of the alnico magnet may even become reversed in step 3.

Perhaps some stray magnetic field coming from the laptop caused the field in the compass needle to weaken and then reverse?

Or here is another possibility. Perhaps somebody took a big magnet to the compass which could also cause the compass needle to reverse? We do have some big magnets in the house and maybe the kids were playing with one of these and the compass at one point.

_http://cse.ssl.berkeley.edu/segwayed/lessons/exploring_magnetism/exploring_magnetism/s1.html

Caution: Compasses can easily change polarity using magnets
It is fun to use the bar magnet to make a compass needle rotate around. However, if while doing this the needle does not move, the polarity (north and south locations) can be reversed. To make the needle point in the correct direction, the polarity of the needle must be such that the arrow points toward Earth’s geographic north when standing outside away from electricity and other magnets. In order to reverse the polarity of the compass needle in a controlled fashion, hold the compass so the needle is horizontal. Then take the bar magnet and move one pole of the magnet length-wise across the compass needle, making sure the needle does not move.

Maybe I'll try this and see if I can get the polarity to flip back to what it was.

Also, it could have just dropped on the floor and reversed.

_http://answers.yahoo.com/question/index?qid=20061015145749AAQsgmj

Anyways, neat little science lesson, fwiw...

 

[RyanX]

_http://cse.ssl.berkeley.edu/segwayed/lessons/exploring_magnetism/exploring_magnetism/s1.html

Caution: Compasses can easily change polarity using magnets
It is fun to use the bar magnet to make a compass needle rotate around. However, if while doing this the needle does not move, the polarity (north and south locations) can be reversed. To make the needle point in the correct direction, the polarity of the needle must be such that the arrow points toward Earth’s geographic north when standing outside away from electricity and other magnets. In order to reverse the polarity of the compass needle in a controlled fashion, hold the compass so the needle is horizontal. Then take the bar magnet and move one pole of the magnet length-wise across the compass needle, making sure the needle does not move.

In case anybody is wondering, this suggestion actually works. I was able to reverse the polarity of the needle this way. It only took about 4 swipes using the north-pole end of a large neodymium magnet to do the job.

Of course, the moral of the story is probably not to depend on cheap compasses for direction in the first place.