how strong does a magnet have to be to demagnetize a credit card?

Answer 1

Sorry, but magnets DO demagnetize credit cards! (Actually, ALTERNATING magnetic field).
However, it depends on the cards magnetic strip quality and the way it has been "written".
Old cards used to be erasable with less than 500 Oesterds, now some safety cards require 3000 Oesterds to be re-written.
A small loudspeaker magnet would erase old cards if passed in the correct alignment with the data path on the strip.
Now you need special heads to write to the cards, with a very strong field. (Values of magnetisation are kept confidential, especially by banks!).
Don't absolutely believe those MythBusters: they are wrong quite a few times...

Answer 2

It would depend on several factors including the type of magnet, the distance the magnet was from the card, and the length of time it was kept in proximity. Also, magnetic 'strength' is measured in several different ways. Make no mistake about it, if you place an anisotropic ceramic magnet near your credit card, it will demagnetize it and render it useless. The capacity of a magnet to demagnetize (and magnetize) things around it is referred to as its 'coercive' property. I hope this helps.

Answer 3

i think it was about 800 gauss

Edit: in defense of the Mythbusters, they PROVED that magnets could demagnetize credit cards. it was eel skin walets that could not!

Answer 4

Get a magnet from a microwave oven; it'll do the trick..

anything smaller than that - u can forget about it.

Watever mythbuster said - screw them.

Answer 5

Myth buster busted it...magnets dont demagnetize it...they might theoretically but pratically they proved that it doesnt

Answer 6

This question had been answered by Mythbuster.
If I remember it clearly, it doesn't de-magnetize it. People are just saying it.