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Magnetic mysteries: 6 answers about magnets' impact on credit cards

A physicist separates fact from urban legend about magnets and credit cards

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Can cell phones erase the data on a credit card's magnetic stripe? How about MRI machines or those magnets that keep your purse closed? And just what exactly is the deal with eel skin wallets?

MEET OUR EXPERT
Dr. Diandra Leslie-Pelecky

Name: Dr. Diandra Leslie-Pelecky
Title: Professor of physics, University of Texas at Dallas
Expertise: Magnetic nanoparticles, nanomedicine, science education for the public and more.
Work with magnets: Her "nanomedicine research explores magnetic nanoparticles that can 'stick' to cancer tumors for a bull's-eye delivery of chemotherapy right to the tumor instead of the more invasive treatments now required."
Gearhead tendencies: She wrote "The Physics of NASCAR: How to Make Steel + Gas + Rubber = Speed," a plain-English explanation of the science behind the sport.

Source: University of Texas at Dallas

We took these questions and others to a physics professor in search of the truth. What we found was that most things that our readers claim erased their credit card's mag stripe actually can do just that -- but they usually only will in extreme cases.

We received several letters from readers in response to our recent stories describing the destructive power of magnets -- ranging from a typical refrigerator magnet to a high-powered junkyard magnet -- against credit cards. (If you missed them, check out "Can a magnet really make your credit card not work?" and ­"Cutting up your credit card the right way" to see what the fuss was about.) Many of you wrote in with your own tales of erased credit card stripes and hypothetical scenarios involving everything from magnetic money clips to cell phones.

Diandra Leslie-Pelecky, a physics professor at University of Texas at Dallas, joined us as a guest expert to help answer some of your most burning questions. Here's what she had to say:

CreditCards.com: We had several readers write in to say they had experienced loss of credit card data on the stripe when exposed to cell phones. Is there any truth in this, and if so, how does this work?

Diandra Leslie-Pelecky: "Any magnetic field can erase a credit card. The bigger the magnetic field, the more likely that you're going to erase the data. Cell phones do have a magnetic field, but it's pretty low."

CreditCards.com: One reader had an MRI and said each one of his credit cards was deactivated after the experience. What caused this to happen?

Leslie-Pelecky: "The fields used for an MRI are huge compared to [all the other scenarios]. They tell you to leave everything outside the MRI -- if this guy wasn't told to do that, the technician wasn't doing her job. The magnetic field is so strong that if you put a screwdriver in the room, it will draw the screwdriver across the room to the magnet."

CreditCards.com: How about the magnetic closures on handbags?

Leslie-Pelecky: "I can tell you from personal experience, oh, yes. They will erase a credit card really quickly. I had a handbag with a compartment on the outside of the purse that closed with a magnetic closure. I was at a science teacher conference and put my hotel key card [the magnetic stripes on key cards are largely the same as those found on credit cards] in there, and it was erased."

CreditCards.com:  What about magnetic money clips?

Leslie-Pelecky: "If it's a magnet, you run the risk of demagnetizing the card. It's the strength of the field and how long you expose the credit card to the field. With an MRI, it doesn't take long. With a money clip or a magnetic closure on a purse, it's not a big field, but if you leave it long enough, it will demagnetize the card."

VIDEO: Do magnets really make
credit cards unreadable?

Watch this video to learn more about experiments that Cynthia did to test whether a variety of magnets -- including a huge junkyard magnet -- would wipe out a credit card's data.

Or to see what started the debate in the first place, watch the clip below.

CreditCards.com: Can two credit card stripes demagnetize each other -- for example, when a driver's license stripe faces a credit card stripe?

Leslie-Pelecky: "Two cards could, theoretically, erase each other, but it would be pretty unlikely -- much less likely than other situations that we've talked about. If two cards were right next to each other, stripe-to-stripe, and held together for a long time, it's entirely possible they could become demagnetized."

CreditCards.com: We received a few letters about eel skin wallets. Some people swear using an eel skin wallet has deactivated the stripes on their credit cards. Some say this has something to do with electric eels. Is any of this true?

Leslie-Pelecky: "First of all, if you buy eel skin wallets, they are not made from electric eels. You will find eel skin wallets that have magnetic closures, so it's possible that you can demagnetize the card that way. Plus, eel skin is much thinner; the cards are not kept as separated so there is more of a chance of exposure to a magnetic field. But the eel skin wallets do not create magnetic fields."

Other factors can have impact, too
Leslie-Pelecky said another thing to consider is that cards that may first appear to be damaged by items with very low magnetic fields, such as a cell phone or a small magnet, may indeed have suffered physical damage instead, such as a scratch to the stripe.

"People tend to not always consider other possibilities, so if your credit card gets demagnetized, look for scratches -- it's possible that you did something to it physically."

See related: Can a magnet really make your credit card not work?, Cutting up your credit card the right way

Published: March 26, 2010



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