Misc

Thor’s Hammer and Electromagnetism

November 18, 2018

A few years ago I had the opportunity to go on a backstage tour of Disneyland with my trade school.  We had an awesome weekend poking around backstage and learning about how permanent shows differ from the temporary shows we were used to, then, upon learning that we had a few Marvel nuts in our group, our tour guide got us a private Thor experience when the company was promoting the recent release of Thor: The Dark World.

I wasn’t super-into Marvel then, but I enjoyed how excited my friends were, surprised by how detailed the meet-and-greet room was, and tickled by a nice moment when Thor asked a member of our group if they would like to try to lift his hammer and, if so, ascend the throne of Asguard.  To no one’s surprise, only the worthy Thor was able to wield the magical weapon and our party exited the experience with no new royalty among us.

A short time later our guide re-joined us and began talking about the technical aspects of the Thor experience: included in that talk was a mention of the unmovable hammer, which a few of us had already (correctly) guessed was an electromagnet.

Electromagnets are pretty neat: send an electric current through a wire, magic occurs, and you suddenly have a magnet.  Turn off the current and the magnet reverts back to simply a funky-looking device which is only vaguely magnetic.

 

A Brief Review of Magnets

Delving into research for this topic, I determined that magnets get really complicated really quickly.  On a high level, a permanent magnet has a north and a south pole: the north pole is attracted to south poles, the south pole is attracted to north poles, and both poles will reject a second pole oriented in the same direction (north rejects north, south rejects south).  These north and south poles are in turn caused by the orientation of groups of atoms called domains.  Each domain has about 1015 atoms.

Think of a domain as an arrow: a permanent magnet has the arrows pointing in the same direction, while the chunks of metal used in electromagnets have their domains randomly oriented, with arrows pointing all over the place.  The beauty of the electromagnet is that the electrical current roughly sorts through the arrows (like on would sort a messy deck of cards or a pile of papers) and encourages them to orient themselves in the same direction.

A layer deeper is where physics and quantum mechanics comes into play.

 

The Physics of Electricity and Magnetism

No one’s really sure how an individual atom is magnetic.  The best guess is that a magnetic atom has some lonely electrons in a particular location, leading to some lopsided geometry on the atomic level.  Electrons not only whiz around an atom, they spin around their own center while doing so (like the Earth spins on its own axis as it revolves around the sun!).  Electrons can have a spin of UP or DOWN, and will only pair up in its electron shell with an electron of the opposite spin direction: it’s possible that these spin directions (along with some geometry requirements) lead to an individual atom becoming a monopole- having a north or south pole, but not both.

However, monopoles have not been proven to actually exist.  If you cut a permanent magnet in half, it will still have a north and south pole.  Cut it in half again, same thing.  If you continue cutting the magnet, you will continue to find a north and south pole up to and until the magnet is so small that it cannot be measured.  In talking to my physics professor about magnets, he told me that if I was able to prove the existence of magnetic monopoles, I would probably receive a Nobel prize and that I should use the money to buy him a Tesla Model S (but don’t worry, he would pay for the charging station himself).

Putting the magnets aside for a moment and jumping to the somewhat lighter topic of electricity…

An electric current flowing through a wire creates a magnetic field.  And now the physics gets ugly.

Imagine a top view of two lines of evenly-spaced runners going past each other in opposite directions and at the same speed.  Now place yourself in the body of one runner.  Now (because running is a lot of work), imagine that your body (and line of runners) is still and the world is moving around you at the same speed that you were running.  From this perspective, it looks like the opposite line of runners is running really fast and you feel a slight attraction to those runners, because you too would like to be able to run really fast.

Obviously, this is a simplification, but I find it far easier to think about than special relativity, the Lorenz invariance, and any sort of mathematical formulas in general.

This attraction is an electrical attraction, which, because we don’t want to have to think about complicated things, is called a magnetic field.  In summary, an electrical current runs along a wire and creates a magnetic field at a right angle to itself as the individual charges swoon towards a second line of runners.

So, like I said, magnets are complicated.

 

Electromagnets are generally made of a metal (often iron) core tightly wrapped with a wire.  The more coils, the stronger the magnetic field that the wire produces, the quicker the domains in the iron core are aligned, and the stronger the electromagnet.  There is a fairly obvious upper limit here, though: once all the domains are aligned, the electromagnet is at its maximum strength.  To get a stronger electromagnet, one can increase the size of the core (more domains to align and more coils of wire) or increase the current in the wire (creating a stronger magnetic field).  Super electromagnets can be created by sending a ton of current through the wire, while cooling the system to make sure nothing catches on fire.

 

A super electromagnet isn’t something that was used as a neat trick in a meet-and-greet though; a 3” electromagnet can be bought for less than $300 with a strength of over 1,000 pounds.  By putting an electromagnet in the floor and a strong permanent magnet in the top of Thor’s hammer, the actor and crew can easily make a moment of Asgardian magic using the mysterious principles of electromagnetism.

 

 

Further Reading:

CoolMagnetMan’s “Magnet Basics”

StackEchange’s “How Do Moving Charges Produce Magnetic Fields?”

Wikipedia’s “Magnetic Monopoles”

Quora’s “Why Does a Moving Charge Produce a Magnetic Field Around It?”

Quora’s “How Does an Electric Current Generate a Magnetic Field?”

UCSB’s Science Line “Electric Current Producing Magnetic Effects”

2 Comments

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