Magnetism. Magnetizing. Can Big Honking Things Be Magnetized ?

Question

When goofing around with a magnet, one will find that some small stuff (with some Fe in it) will become magnetized (to whatever degree).

What would be required to magnetize something of pretty substantial size - like a fire hydrant or a manhole cover or the side of a car ?

All kinds of stuff could be magnetized - just for laughs - if it's practical to do so. (I don't need admonitions about the potential damage/problems that magnets can cause).

And would it stay magnetized ?

Answer 1

To magnetize something of pretty substantial size, you need a magnet of pretty substantial size. Take a clue from the size of the electromagnets they use in car wrecking yards. Those ought to work fine on fire hydrants.

I'm not sure if any city has ever passed a law against magnetizing fire hydrants and manhole covers. Yes, once successfully magnetized, they should stay that way for a while. Slow exponential decay and all that.

Answer 2

To magnetize metal all you need is electric current, finding the right voltage, amps and ohms would be the only thing you need to find out. You know like when they make electro-magnets (like the cranes at the junk-yards) . if you ran the current long enough for the molecules in the metal to become polarized it would become a electromagnet. staying polorized would be your problem because you would loose the charge when you switched off the juice because of impurities in the metal. Theorocitally if you ran the current through long enough, they would just stay polorized because they are shocked into place. (ever notice if you hit an iron nail with a hammer it gets magnetized from the "shock"?) but iron (fe) is easily magnetized from the structure of it's molecules.