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Don’t try this at home! The experiments and products shown in this episode were used in the name of science.

Creator/Host/Writer/Editor: Dianna Cowern
Editor: Jabril Ashe
Science Consultant: Dan Walsh
Videography: Dianna, Jabril and Trace Dominguez

Thanks to Rachel Cohen for the idea for this video and for her help!

Thank to Casey Wessel, Demetra Airaudi, and Josh from the farmers’ market.

Physics Girl : What Size Magnet Can Erase a Credit Card?



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  1. Contact-less? You mean those things we have had a few years here in Norway, where you just put the card next to the machine to pay?
    You think those are secure?
    Well then, I'll see you in the subway with a payment machine, just innocently moving it around your pockets.

  2. Rust is actually iron hydroxyde. Also, electric and magnetic fields are not the same because electric fields are created by static charges and magnetic fields – by charges in motion. Finally to the point: many cards feature both chip and magnetic stripe making them vulnerable even if only chip is used because malevolent persons can place stripe reader in the slot where card is inserted to use its chip.

  3. I worked with multi-tesla NMR spectrometers and have had experience with erased credit cards. You should know that mag-stripes come in two flavors, low coercivity (natively brown) and high coercivity (natively black). The Hi-Co cards are a lot more resistant to large fields. Very small fields (like your first magnet) have high dB/dt and are really good at erasing mag stripes. Loved the video!

  4. i think the chip lady was full of it. otherwise they wouldn't make rf id blocking wallets, etc.. there are rf id skimmers to people just need to get close enough to you to get it. prob easier than a conventional skimmer.

  5. Why don't they switch to optical if the magnet stripe data is just static barcode data? I know chips are taking over and stripe thing is obsolete but they still put magstripes today on the cards as a secondary method. Why not optical?

  6. I don't know if you have any experience with Samsung Pay, but this is what Samsung phones use for its contactless payment. That's why it can work pretty much anywhere, because it changes the magnetic field to make a card swiper think a card has been swiped. Really cool video though, I understood how Samsung Pay worked but the part where you stuck the particles to the credit card really helped visualize why it's ultimately possible!

  7. I’m from Chile and we made the move to chips and contactless tech few years ago, and our bus/metro pass has always been contactless. However, watching this video I’ve remembered the time I “deleted” the info on my pass by keeping both my phone and pass in the same tight pocket. Also last year there was a huge issue with contactless tech here bc the range in which the card could be read (by different devices) was wider than expected (card-kept-in-a-wallet-inside-a-bag wide). So it might be fun to find other culprits on our damaged cards!

  8. What about the long term effect of exposing the magnetic strip for long periods of time to weak magnetic fields, like the speakers of a tablet in a suitcase or the magnetic lock of a purse and so on?


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