Permanent magnets are always magnetic, unlike electromagnets which require an electric current. They are made of substances like magnetite or neodymium and have two poles, north and south. They have many uses, from refrigerator magnets to electric motors, but can also be a nuisance, erasing data from ATM cards and hard drives.
A permanent magnet is a permanent magnet, unlike an electromagnet, which only behaves like a magnet when an electric current is passed through it. Permanent magnets are made up of substances such as magnetite (Fe3O4), the most magnetic mineral found in nature, or neodymium, a powerfully magnetic synthetic substance. The Earth itself is a huge permanent magnet, although its magnetic field is quite weak for its size. Humans have used the Earth’s magnetic field for navigation since the compass was invented in ancient China.
Even the strongest permanent magnet is not as strong as the strongest electromagnets, so their applications are limited, but they still have many uses. The most mundane would be use as refrigerator magnets, but magnets can be found everywhere, including hard drives, ATM and credit cards, speakers and microphones, electric motors and toys. Electric motors work through the interaction between an electromagnet and a permanent magnet.
Each permanent magnet generates a magnetic field, just like any other magnet, which circulates around the magnet in a distinct pattern. The size of the magnetic field is related to the size of the magnet and its strength. The easiest way to visualize a magnetic field generated by a permanent magnet is to scatter iron filings around a bar magnet, which quickly orients itself along the field lines.
Every permanent magnet has two poles, called north and south, although they could just as easily have been called A and B. Like poles repel while opposite poles attract. It takes a great deal of effort to hold the repelling poles of a magnet together, while it takes effort to remove the attracting poles. Stronger magnets attract each other so strongly that they can cause injury by pinching the skin together.
For thousands of years, permanent magnets were the only magnets humans had. The electromagnet was only invented in 1823. Before that, magnets were mostly novelties. Using an electromagnet, a current can be induced in any ferromagnetic material, such as an iron paper clip. However, the effect wears off quickly.
Permanent magnets can be a nuisance threatening to erase data from ATM cards or computer hard drives. A common way to erase data from a computer’s hard drive and make sure it’s unrecoverable is to swipe a magnet over it. Otherwise, the “deleted” files actually remain on a computer, just hidden. This is because it takes more effort for the computer to actually delete the data. Rather, the data is designated as a sector of the hard drive that can be safely overwritten.
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