Woozers! How did I miss this thread?

My 1/2 cent - I keep my magnetic office access card in my shirt pocket. I very occasionally put my cell in there too. When I pulled the phone out once, the plastic card was stuck to the phone. Next time I attempted to access my office - no dice - something in the phone wiped out the magnetic strip embedded inside the card.

On the good side - I can now open doors with my Droid! They ought to have an app for that.

wow


Funny how I can still remember the correct technique to do a propor keg stand

Metal Detectors:

I’d like to just say a final word about the use of metal detectors and how it might affect your watch. Most metal detectors use an oscillatory generator to produce very short, alternating magnetic fields which are used to detect magnetic metals. Even more advanced designs which can use more severe magnetic energy don’t pose a significant risk to your watch. The alternation of field direction and relative weakness mean that there is little chance your watch will become magnetized. I wouldn’t suggest you try it, but the occasional swipe at a sporting event/airport won’t hurt.

I decided to put together a little primer on the electromagnetic spectrum and magnetism because I’ve seen a few posts around the forum about exactly what can and cannot magnetize your watch. Despite what my current avatar and signature might suggest, I am no Albert Einstein. I am just looking to make a few distinctions about commonly confused elements in physics and maybe dispel a myth or two. I’ve had the “pleasure”, as others on this forum have, to have been through too much physics education in college. I tutored the subject while a senior and also currently teach basic science education to elementary school students on a volunteer basis. If that doesn’t qualify me to give a lesson to you lot, then I don’t know what does! Only kidding! Please feel free to correct, reprimand, and add to this post! I am not the end-all, be-all on this subject.

For those who are unaware, when a watch becomes magnetized it is primarily the hairspring which is affected (guys, correct me if I'm wrong). The hairspring, when magnetized, functions improperly. Instead of freely coiling and re-coiling, there is a magnetic attraction that occurs, effectively tightening the hairspring and thereby shortening the period of the timepiece. This, in turn, dramatically increases the rate of the watch. As I’ve read here, on the order of minutes-per-hour fast. The only way to “magnet-proof” a watch is to completely remove any component that is susceptible to magnetic field.

So, off to the physics races!

What’s in a name?
There are two main concepts that I’ve seen most often purported as the culprit behind watch magnetization:

1) Components of the “Electromagnetic Spectrum”
2) Magnetism and electromagnetism.

Despite their name both involving some form of the word “magnet” there is very little in common with these two concepts. I will describe this a bit further as I go along, but if there is one thing you can garner from this post, it’s that no component of the electromagnetic spectrum is responsible for magnetizing your watch. It is only relatively strong magnetic fields in close proximity to your watch that can result in a magnetized movement.

What is the Electromagnetic Spectrum?

The electromagnetic (EM) spectrum is merely a map of known levels of radiation, ordered by wavelength (size). Radiation is a general term here which describes the wave form of energy emitted by celestial bodies, radioactive material, and other energy sources. Below is an example of the EM spectrum taken from Wikipedia.

http://upload.wikimedia.org/wikipedia/c ... s_edit.svg

The EM spectrum is ordered from the biggest, lowest energy waves (left), to the smallest, highest energy waves (right). You will certainly recognize a fair bit of the categories: microwaves, radio waves, visible light. We are literally bombarded by billions and billions of these waves in a day (please don’t call me Cark. Sagan). Almost all communication and detection devices employed today use some small sliver of the EM spectrum. This includes almost every medical and security scanning devices aside from Magnetic Resonance Imaging (MRI).

While certain portions (generally, the higher energy region) of the spectrum can have disastrous health affects and can literally disintegrate matter, there is no mechanism by which these waves can produce a magnetic field. Your watch, with respect to magnetism, is unaffected by the EM spectrum.

Magnetism and Electromagnetism

Types:
Magnetic objects come in three basic flavors:

1) Permanent Magnets
2) Temporary Magnets
3) Electromagnets

All of these pose a significant risk to your watch because they can be of sufficient strength to magnetize the internals of the movement. If you allow your watch to get close enough to any one of these you might be in trouble.

Essentially all three types rely on the alignment of negative and positive regions of an atom to create a magnetic effect. It has specifically to do with electron spin but for purposes of illustration, I’ve shown picture of a simplified magnet. A magnet is born when all of the positive and negative regions line up.



Some materials have regions of positive and negative charge lined up inherently. These materials are called permanent magnets. These magnets will not lose their magnetism without a fight. These are the ones found most commonly around the house as refrigerator magnets and in consumer electronic devices. These magnets are an integral part of speakers of any size, hard drives, etc. They pose a real risk to your watch.

Materials, like soft steel, can be turned into temporary magnets by aligning the positive and negative regions. If you’ve ever run a magnet over a paper clip repeatedly, you’ve created a temporary magnet. Because their normal configuration is non-magnetic, it doesn’t take much to return these to their non-magnetic state. This type of magnet can still pose a risk to your watch because, when aligned, can still be fairly strong.

Finally, the most interesting type of magnet, IMO, is the electromagnet. This is a magnetic field which is induced by the application of current through a coil of metal wrapped around an iron core. The flow of electricity actually artificially aligns the positive and negative regions in the material and induces a magnetic field. This phenomenon is used in conjunction with permanent magnets to generate electricity as well as serve a means to create efficient electric motors. These magnets can become very powerful as they are limited only by the current applied to the coil itself. As another user posted noted here: http://www.breitlingsource.com/phpBB2/viewtopic.php?f=6&t=16460

Walking into a room with a generator in it is a big no-no for your watch.

Magnets all have fields associated with them. One of the best ways to visualize those fields is by use of iron filings. Here is a picture from Wikipedia of just such an illustration.



Proximity:

How close you can get to a magnet depends on its strength. The closer you get to a magnet, the more intense the field strength becomes. As a general rule I’d suggest not placing your watch directly on or directly next to anything you might suspect is magnetic. Just moving 6 inches away from a relatively strong magnet can dissipate real risks of watch magnetization. The field strength increase when you approach the source is exponential.

Metal Detectors:

I’d like to just say a final word about the use of metal detectors and how it might affect your watch. Most metal detectors use an oscillatory generator to produce very short, alternating magnetic fields which are used to detect magnetic metals. Even more advanced designs which can use more severe magnetic energy don’t pose a significant risk to your watch. The alternation of field direction and relative weakness mean that there is little chance your watch will become magnetized. I wouldn’t suggest you try it, but the occasional swipe at a sporting event/airport won’t hurt.


If you've made it to the end of this, I apologize for the length! I never intend for these to get so out of hand but sometimes I just can't help myself. I hope this helps answer more questions than it poses in your mind.