Tool Demagnetizers And The Magnetic Stray Field

If you’ve ever found yourself wondering how those tool magnetizer/demagnetizer gadgets worked, [Electromagnetic Videos] has produced a pretty succinct and informative video on the subject.

The magnetizer/demagnetizer gadget after meeting its demise at a cutting disc. (Credit: Electromagnetic Videos, YouTube)
The magnetizer/demagnetizer gadget after meeting its demise at a cutting disc. (Credit: Electromagnetic Videos, YouTube)

While the magnetizing step is quite straightforward and can be demonstrated even by just putting any old magnet against the screwdriver’s metal, it is the demagnetization step that doesn’t make intuitively sense, as the field lines of the magnets are supposed to align the (usually ferromagnetic) material’s magnetic dipole moments and thus create an ordered magnetic field within the screwdriver.

This is only part of the story, however, as the magnetic field outside of a magnet is termed the demagnetizing field (also ‘stray field’). A property of this field is that it acts upon the magnetization of e.g. ferromagnetic material in a way that reduces its magnetic moment, effectively ‘scrambling’ any existing magnetization.

By repeatedly moving a metal tool through this stray field, each time further and further away from the magnet, the magnetic moment reduces until any magnetization has effectively vanished. It is the kind of simple demonstration of magnetism that really should be part of any physics class thanks to its myriad of real-world uses, as this one toolbox gadget shows.

9 thoughts on “Tool Demagnetizers And The Magnetic Stray Field

  1. One of the first things I built from scraps as a kid was an AC powered magnetizer/demagnetizer.

    Enclosure from a broken rectangular alarm clock, some weird embossed aluminum from some discarded beauty shop equipment, a scrapped solenoid coil from some industrial holding latch that my hrandpa gave me, and a power cord from who knows what, and a microswitch from another forgotten source.

    Stick the screwdriver through the rectangular hole hacked in the side of the clock case, tap the snooze bar on top and the screwdriver was miraculously magnetic.

    Put the screwdriver in the same hole, hold down the snooze bar while pulling the screwdriver out and no more magnetism.

    I still have that thing somewhere.

    They probably shouldn’t have let a little kid build something like that. On the other hand, I never asked.

    Not all projects were as successful though. Burned stuff, learned stuff.

  2. The Explanation in the video of [electromagnetic videos] is nice and clear.
    But could be more practical. I recently was looking for a way to demagnetize my tools , as I wanted to repair a video deck. My tools often came too close to some large loudspeaker chassis.
    I found this interesting video:
    it demonstrates how effective the magnetizer demagnetizer tools are ( not too well) and shows a way to reuse some old transformers to do a better Job.

    1. Yeah, was gonna say it sounded familiar. I guess it’s a statistical inevitability that different creators will end up making videos about the exact same topic… Maybe think of [Brainiac75] and [Electromagnetic Videos] as complimenting each other’s videos to give a fuller view about the thing?

  3. The demagnetizer section is incorrect. It is about the direction of the field lines and orienting the domains in the steel shaft nice and long lengthwise versus short and weak across the rod. The stair-step runs it through different sections of the curving fields and increases the confusion.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.