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Magnetic Stripe

June 4, 2008

A listener asks why credit cards with magnetic stripes don’t stick to the fridge.


Why magnetic stripes don’t stick. I’m Bob Hirshon and this is Science Update.

Listener Joel Haglund wrote to ask why the magnetic strip on the back of a credit card doesn’t stick to the fridge. We asked physicist Greg Boebinger, director of the National High Magnetic Field Laboratory at Florida State University. He explains that a magnetic stripe contains strings of code made of tiny magnetized particles. Each particle creates only a very small magnetic field.

GREG BOEBINGER (National High Magnetic Field Lab, Florida State Univ.):
When you swipe the card, something actually rubs along the surface of the card to even detect that field. So the magnetic field of the credit card does not extend much beyond the credit card. And in addition, it’s quite weak.

… Far too weak to hold the weight of the credit card on a vertical surface. Boebinger also notes that even a fridge magnet could potentially scramble a magnetic stripe card, making it unreadable. I’m Bob Hirshon for AAAS, the Science Society.