to read the magnetic strip on an credit card, you must swipe it quickly past a tiny coil of wire.?
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When you move the card through the reader pulses of current (not voltage) are generated in the coil(s) which reads your card (the Faraday effect).  The more quickly the card moves through the reader, the higher amplitude current is generated.  If you move the card too slow, the current generated is too small, and then the electronics attached to the read coil(s) cannot see a signal large enough to be detected as pulses which are interpreted as the 1's and 0's of the data on your card.\nTry the first link below and move the magnet slowly and quickly and observe what the difference is on the meter.
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look  for what is a magnetyou will find out a lot of stuff
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Look on the back of the card for a website
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Induction. \n\nWhen you wind a conductive wire into a coil and pass a current through it, you create a magentic field that extends from the coil.  Similarly, if you hold/move a coiled wire in a magnetic field, you "induce" a current flow in the coil.  With AC, there's no need for the coils to move relative to one another. (That's how a transformer works)  The toothbrush base has a coil in it, and the AC coming out of the wall goes through a coil in the base, induces current in the coil in the toothbrush, and that current charges a cell in the handle.\n\n Here are some neat links:\n\nhttp://www.energyquest.ca.gov/how_it_works/transformer.html\n\nhttp://micro.magnet.fsu.edu/electromag/java/faraday2/
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start here:\nhttp://en.wikipedia.org/wiki/Magnet
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Take away its credit card
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Conduction?  I'm not aware of magnets having such a property.
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With a Magnetometer. See below for more detail.
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Radio Frequency Identification (RFID) cards contain tiny transceivers which are activated when the pass near a sensor.\n\nSome are self-powered (active), with a tiny built-in battery but most are "passive" cards, powered by an induced current from the sensor unit. Active cards have a much greater range and must be used whenever distance from the sensor is a factor. This generally is not an issue for proximity card applications.\n\nRFID chips can be read-only -- a simple fixed code is transmitted which identifies the card or product -- or read-write, where information contained on the card or tag can be modified.
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There are some natural magnets. For example, the mineral magnetite is magnetic, and is found in lodestones. \n\nIf you have a magnet, you can stroke a piece of metal (not all metals, but some) and magnetize it; that is, turn it into a magnet. You line up the magnetic domains when you stroke it so it has a net magnetic field. If you put a radio reciever nearby tuned to the right frequency, you can hear the domains flip as you do this; this is called the Barkhausen effect. \n\nThere are also electromagnets. Passing an electric current through a coiled wire wrapped around the right kind of metal (called a shunt) produces a magnet. This is the kind of magnet one finds in MRI machines.
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Depending upon your application, copper probably does not make a good coil core.  If you wrap many turns of wire around a steel nail and pass a current through the wire (say from a battery) the nail will concentrate the magnetic field and you will have an electromagnet in which the tiny magnets within the steel are all aligned.  This will not happen with copper because you can not pick up copper with a magnet.  The coil will still produce a magnetic field but the copper core will not concentrate it.
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The stripe on the back of a credit card is a magnetic stripe, often called a magstripe. The magstripe is made up of tiny iron-based magnetic particles in a plastic-like film. Each particle is really a very tiny bar magnet about 20 millionths of an inch long.\n\nThe front of your credit has a lot of numbers. Here is an example of what they might mean.\n\nYour card also has a magstripe on the back and a place for your all-important signature.\n\nThe magstripe can be "written" because the tiny bar magnets can be magnetized in either a north or south pole direction. The magstripe on the back of the card is very similar to a piece of cassette tape fastened to the back of a card. See How Cassette Tapes Work.)\n\nInstead of motors moving the tape so it can be read, your hand provides the motion as you "swipe" a credit card through a reader or insert it in a reader at the gas station pump.\n\nThere are three tracks on the magstripe. Each track is .110-inch wide. The ISO/IEC standard 7811, which is used by banks, specifies:\n\n    * Track one is 210 bits per inch (bpi), and holds 79 six-bit plus parity bit read-only characters.\n    * Track two is 75 bpi, and holds 40 four-bit plus parity bit characters.\n    * Track three is 210 bpi, and holds 107 four-bit plus parity bit characters. \n\nYour credit card typically uses only tracks one and two. Track three is a read/write track (that includes an encrypted PIN, country code, currency units, amount authorized), but its usage is not standardized among banks.\n\nThe information on track one is contained in two formats -- A, which is reserved for proprietary use of the card issuer, and B, which includes the following:\n\n    * Start sentinel -- 1 character\n    * Format code="B" -- 1 character (alpha only)\n    * Primary account number -- up to 19 characters\n    * Separator -- 1 character\n    * Country code -- 3 characters\n    * Name -- 2-26 characters\n    * Separator -- 1 character\n    * Expiration date or separator -- 4 characters or 1 character\n    * Discretionary data -- enough characters to fill out maximum record length (79 characters total)\n    * End sentinel -- 1 character\n    * Longitudinal Redundancy Check (LRC), a form of computed check character -- 1 character \n\nThe format for track two, developed by the banking industry, is as follows:\n\n    * Start sentinel -- 1 character\n    * Primary account number - up to 19 characters\n    * Separator -- 1 character\n    * Country code -- 3 characters\n    * Expiration date or separator -- 4 characters or 1 character\n    * Discretionary data -- enough characters to fill out maximum record length (40 characters total)\n    * LRC -- 1 character \n\n\nThere are three basic methods for determining that your credit card will pay for what you're charging:\n\n    * Merchants with few transactions each month do voice authentication, using a touch tone phone.\n    * Electronic data capture (EDC) magstripe card swipe terminals are becoming more common -- so is having you swipe your own card at the checkout.\n    * Virtual terminal on the Internet \n\nThis is how it works: After you or the cashier swipes your credit card through a reader, the EDC software at the point of sale (POS) terminal dials a stored telephone number via a modem to call an acquirer. An acquirer is an organization that collects credit authentication requests from merchants and provides a payment guarantee to the merchant.\n\nWhen the acquirer company gets the credit card authentication request, it checks the transaction for validity and the record on the magstripe for:\n\n    * Merchant ID\n    * Valid card number\n    * Expiration date\n    * Credit card limit\n    * Card usage \n\nSingle dial-up transactions are processed at 1200-2400 bps, while direct Internet attachment uses much higher speeds via this protocol. In this system, the cardholder enters a personal identification number (PIN), using a keypad.\n\nIf the ATM isn't a
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You need to run LOTS of current through a coiled wire. For a strong one I don't know, but you can make one big enough to deflect a compass like this:\n\nWind some stripped copper wire around a pencil to make a coil. Then connect a D cell battery to the wire. The important thing is that voltage doesn't matter, the stronger the current in the wire, the more powerful the wire.
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a what???? You want to fish for magnets or paperclips or what? I have a vague idea how you could do this though, but I would need to know what you mean....
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Do you mean "magnetic"?????
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There are a couple ways I've found after going through several of my college IDs...\nMagnetic strips do not mix.  If you keep all your cards together, they can demagnetize each other.  Make sure to keep them in a wallet or separate them somehow.\nSecondly, don't put your credit cards in contact with a floppy disk (although now nearly obsolete).  I used to keep everything in my back pocket or backpack, and these things frequently came in contact.  Your magnetic strips will demagnetize if in contact with anything else magnetic.\nThere's also those security devices at some checkout counters, mainly for purchases like CDs and such.  The cashier will swipe your purchase over them so as not to set off the security alarm when you leave.\nFinally, sometimes these strips can just wear out.\nHope this helps!  :)
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I was wondering myself.  So, when no one answered I decided to do some research.  I found several explanations that did not make sense.  But I did locate some credible sources.\n\nThe first reference gives technical information on encoding the magnetic strip.\n\nThe second provides confirmation that noise from scratches or defects in the magnetic strip induces spikes in the reader that can be misinterpreted as valid data.\n\nThe third provides an explanation in layman's terms that is consistent with the more technical explanations.  The following quote is from this source.\n\n"Let's just say that when you swipe the card through the reader, the magnetized particles in its stripe generate a signal with "ticks" in it at intervals that the machine is able to interpret as digital ones or zeros. A scratch or other defect in the magnetic stripe can cause a spike (i.e., brief fluctuation) in the signal that a too-sensitive reader will interpret as a tick, meaning that the encoded data will fail the parity check (the numbers won't add up right) and the card won't work. Wrapping the card in plastic increases the distance between the read head and the magnetic stripe, thus reducing the strength and crispness of the signal and smoothing out anomalous fluctuations. Behold, the card works."