Somebody gave me a book entitled The Compass in your Nose, which claims that there is some magnetic sensitivity in the human body:
I’ve never see n any corroboration of its claims, though. And certainly never felt a magnetic yank on my honker, despite working with some high magnetic fields through the years.
A bit more on this:
Magnets repel diamagnetic materials, though weakly. This is one basis for levitation, and the basis specifically for frog levitation. Water is fairly diamagnetic. Pyrolytic graphite is barely diamagnetic enough to levitate a piece stably on top of a neodymium iron boron magnet. Bismuth, a lead-like metal often used as a safer replacement for lead, is diamagnetic enough that a rod hanging on 4’ of string can be held a half inch out of plumb by a strong magnet (I have the bismuth rod, string, and magnet to do this and have set it up in the basement for fun). The forces involved are pretty small, and I can’t feel them, but I wonder if somebody with very sensitive hands or skin might be able to.
I read that MRI’s sometimes cause people to see little bright spots with their eyes closed. I forget what these are called, it’s not “phonemes” but I think it’s something similar. You can also sometimes see these spots by closing your eyes and pushing on them through the lids. I think they are artifacts caused by disturbing the retinas, and they’re harmless, at least if you aren’t too aggressive about it. I’ve had several MRIs and never seen them, though.
Phosphenes:
Why the hell wasn’t I informed that frog levitation is a career choice? :mad:
Those posers at career day in High school who never mentioned that are gonna hear me.
Doesn’t MRI remove your metalic eye shadow? You would feel that.
(Yes, that would only have been done by people testing the machines. I’m sure they have people remove all makeup just to avoid odd shadows in the images)
The iron in your bloodstream is in individual atoms of iron bound up inside a hemoglobin molecule. Whereas iron’s magnetism is really a result of iron’s behavior in bulk, when lots of atoms line up and all point in the same direction.
So the iron in your blood isn’t that much more magnetically sensitive than the water in your blood, or many other things in your body. A really, really, really, strong magnetic field will start affecting various things (such as levitating frogs), but the iron won’t be particularly more affected than anything else.
I hope I never have to get an MRI now. The poor tech is bound to think the machine is making me laugh hysterically.
1920’s style deaf rays, indeed.
I’ve had my hand inside the bore of our lab’s 12T superconducting magnet. Nada.
(By comparison, modern high-end MRIs are 3T.)
I’ve had metal shavings in my eye before (since removed). Before I had an MRI, they did an X-ray of my eyes to make sure there were no lingering bits of metal still in my eyes. As for feeling anything during the MRI, nope.
So what, exactly, does standing near a large radio transmitter feel like?
Our local public radio system made a documentary about the workers who do maintenance on transmitter towers. That very question came up. The guys said they were very careful to assure that the transmitter power was lowered to safe levels before approaching too close, but they added that mistakes had occurred. They said that they could feel a warmth in their bodies and still had time to retreat and/or communicate that there was a problem.
Or in a running washing machine that’s being attacked by a road crew with jackhammers. Described in one word, an MRI scan is LOUD.
And add me to the crew that’s never felt anything unusual while in the bore of a 3T scanner.
eta:
Ask your lunch the next time you pop something into the microwave oven.
Depending on things like power level and AM vs FM, it’s a variously warm/prickly sensation all over your skin, and generally unpleasant. There’s actually been some work done on directed RF weapons as a “less than lethal” method of crowd control and deterrence.
What about peiceings? I had to take my eyebrow peiceings out and they aint madnetic. and it was only my ankle that was going into the machine!
So that trick Magneto did by pulling all the elemental iron out of a guy’s bloodstream–? Total fantasy… I will sleep better knowing my hemoglobin is safe from X-Men.
Well, they injected a large amount of iron into the guy earlier in the movie.
Ona account of the sensation can be found in here.
This is exactly how the microwave oven was invented. Some dude was working on a microwave transmitter, and the chocolate bar in his pocket melted.
50 years later, and we can make popcorn in seconds! What a country!
I seem to recall reading in a reputable source (or at least I thought so at the time) that one of the first people involved in microwave technology was so in love with the idea that he would heat his home with microwaves, and guests would report a rather strange warm sensation upon entering his house. Does this story sound familiar to anyone, and is it true?
My brother maintains CAT and MRI gear for a living. Magnets that size will have an effect on non-magnetic metals. If you stand an aluminum sign on edge inside the magnet, it will take a minute or two to slowly fall over. When I was inside the magnet, though, my numerous fillings did not feel unusual.
In the cold war era, some dental work in the communist countries was done in iron. If you meet a guy with a rusty-capped tooth, that’s where he’s from.
The machine I was in sounded like a slow drum roll on a saucepan. My brother said the noise was the scanners moving a small distance, then locking, again and again. It has to be precise, or the scan will be slightly off, and useless.
I know a guy with an artificial heart valve. Although it’s made of titanium and plastic, he was warned to never have an MRI.
>Why the hell wasn’t I informed that frog levitation is a career choice?
This may not have been made clear, but it’s only a career choice for frogs, not people.
You know, we’re not talking a wide enough range in field strengths here. MRI machines today generally have a field strength in Teslas that is equal to their price in millions of dollars. I think maybe 0.9 and 3 T machines are fairly common and there are some 9 T machines here and there.
Neodymium iron boron magnets have field strengths of around 1 to 1.5 T at their pole faces, I think.
It is lots of work to create tens of T. Crescend has acces to a 12 T superconducting solenoid bore, making him luckier than most, and reports nothing.
A friend used to work at the Bitter lab at MIT, where they generate I think around 30 T using high strength coils wound of a silver-copper alloy. They aren’t superconducting. They’re cooled by air or water flowing by at high speed. The power consumption is such that they have to coordinate throwing their switches with the local power company.
So, none of these things is very dramatic to feel, unless you are very small or sensitive.
If a field is changing, you may feel consequences of the currents that can circulate. I was once pretty startled during a MRI scan when my wedding ring started vibrating on my hand, and hit the emergency button because I thought I had forgotten to take it off and was going to cause trouble - turns out they no longer ask people to remove them, unlike my earlier MRIs, at least at this place.
Now, objects like magnetars have higher field strengths, many orders of magnitude higher, and all sorts of things would be different in a field like that. So, I’m sure the answer to the OP is that you CAN feel some magnetic fields, and in fact get vaporized or timewarped or something, but maybe not by any fields available to people today.