Magnetic Hysteresis or I KNOW WHAT YOUR MAGNET DID LAST SUMMER | Doc Physics

When I was your age, kids played with magnets and threw scissors at each other instead of texting. It was a simpler time.

You probably are wondering what distinguishes hard and soft magnetic materials from each other. Well, this is it.

Here are some ways to spell hysteresis wrong: histeresis, hysterisis, hizthérèsez, histeriasis, hystirysis, hystirisis. Can you come up with more?

[nathan]

You are seriously a life saver! So refreshing to have someone explain colloquialy... This is how you explain a concept well and quickly.. I dont understand people who try and overcomplicate concepts for nothing

[ahorsewithnoname]

I don't know how I ended up here, but that was the most educational 20min of my life. I love when someone is able to explain and demonstrate a topic so well that you're left thinking at the end "yeah, I already knew all of those concepts." Yet collectively you have never put them all together to make a cohesive thought or conclusion. Thank you for explaining.

[oostyx]

i picture this guy rolling into class on a skateboard wearing a backwards cap.

[power-max]

YES, Finally a worthwhile video explaining concepts like thin an *engaging* way rather than some old fart in the distance on a green chalkboard moaning on hour an hour and a half, You have rightly earned my subscribe!

[alperentopay]

I wish there was more of you at our college of engineering. Would make life so much easier.

[Roberto-dony]

You know how to teach unlike my lecturer!! thank you so much, and the humour helps remember the concept even better :)

[Anya-tyoh]

This is like the best explanation of hysteresis. If teachers taught physics this way, the world would have been a better place.

[xavierturano]

AT THE END OF THE VIDEO I REALISED I DIDNT HAVE TO TAKE ANY NOTES BECAUSE YOU TAUGHT WELL ALL THE ANALOGIES AND THE ENERGY YOU HAD WAS ENOUGH TO BURN WHAT YOU SAID INTO MY HEAD. A SOLID 10/10 WELL DONE

[shikamaruX]

this was beautifully and hilariously explained, thank you

[kalmahnalyd]

Why don't I have a teacher like you in my school?
You're awesome man!

[victordolman]

I always find hysteresis scary. It reminds me of how lucky we have been so far that it is not real. Actual, fundamental hysteresis would be a devastating blow to physics. Not fatal maybe, but an enormous setback. Sharing my fear makes me a little less afraid, so that is what I'll do.

A basic feature of fundamental theories, classical Newtonian or quantum mechanical, is that it is possible in principle to specify an initial state of a system, and then the theory (again in principle) tells us everything about the future of that system. This also applies to spin, so one might wonder how ferromagnetic hysteresis is possible at all. The fundamental equations (say a many particle Schrödinger equation with magnetic interaction terms in the Hamiltonian) simply allow any initial state to evolve uniquely in time. So there should not be any hysteresis at all.

The answer is basically this video. The story you tell shows explicitly how hysteresis does NOT occur, but is only apparent. If we think that the state of a piece of iron is adequately specified by giving its (unperturbed) magnetic field, we are mistaken. The configuration of the domains and their boundaries is also an essential  part of the state of the system. If we choose to ignore them, we will not have a unique time evolution. If we take them into consideration, as you do in the video, the whole system becomes an ordinary case of a state whose future depends on the current state, but not on its past. You go through it, step by step. So thank you for showing the absence of hysteresis :-)

In a few minutes I'll go to bed, switch off the lights and try to sleep, if I can. But I'm not sure I can. Suppose there would actually be hysteresis that no one can explain away by including more properties into the state, as you did. Then the future of a system would actually, really, unavoidably, depend on its (entire) past. Quantum mechanics would be wrong, and so would Newton. The whole mechanism of partial differential equations would not be relevant to physics. We would, in short, have almost nothing in the way of physical theory. When I imagine this, I cannot help but feel horror.

Thank you for listening to my fear. It really helps. Goodnight. :-)

[anamendoza]

First year of chemical engineering at taipei, videos like these are my saving grace. God bless you😂

[abbas_oso]

this dude is insane
why don't we have more educational content like this these days

[doudsbass]

Nice, especially your clicking device 😁 Also a remark about your voting people analogy for the micro/macro organisation of magnatised objects : I liked it, I think Theoria Apophasis (Ken Wheeler) would call that coherency and point source. You might like his very simple Physics based on pressure mediation in the Eher (inertia and losses of inertia). It's kind of piratry for current scientists but he says that Tesla and Steinmetz already said similar things. Anyway, thanks for the lesson 😊

[Shahriar]

My god!
All these years I've been hearing "Physics is Fun!"
Now I definitely know why!!! Thank you Doc!

[harshuttarwar]

holy.. only if I had a teacher as cool as you.. never understood a concept better.. beautiful way of teaching man.. you earned a subscriber!!

[joaogonzalez]

Hi Doc, I came across you video here, very nice introductory view about magnetic momentum and domains. Just want to freeze one thing, as you know "saturation" (B=nM) is only theoretically achieved and for most ferromagnet materials, even for non soft ferrites, will not align all domains in a "saturation" scenario as you described here :) . Good job.

[faridmammadov]

Explanation is awesome but there was a huge mistake at the very end of video from 20:00-20:10. It is not the residual magnetic flux density Bres which distinguishes the hard and soft magnetic materials. It is the coercive force i.e. magnetic field intensity Hc distinguishes the hard from soft magnetic materials. The wider the graph in lets say x direction the more the harder the material from magnetic point of view.

[tiana]

This is absolutely delightful and brilliant. I'm cracking up and learning so much :D

[DougLand]

I watched a few of your videos. They may take a while to finish because they are so comprehensive because of the subject matter. But when I get to the end of the video, I seem to love hitting the AH-HA moment. Keep it up!