[ 1 ] Magnets are objects that either attract or repel other objects. Every magnet is surrounded by a force called the magnetic field. It is this field that will act on other objects. Magnets have a north pole and a south pole. The north pole of one magnet will be attracted to the south pole of another magnet. Just think of the saying “opposites attract.” Also, the north pole of one magnet will repel, or push away, from the north pole of another magnet. Magnets can even be combined and stacked to create a stronger magnetic field.
[ 2 ] Magnets are named because naturally occurring magnets were discovered in a place called Magnesia, in Asia. The magnets there were actually part of rocks, and scientists noticed that the rocks would attract other metal objects. Naturally occurring magnets are called lodestones. Most of these rocks contain iron that has been permanently magnetized.
[ 3 ] Most iron is not a permanent magnet, but it can be made into a temporary magnet. Iron is a metal we use to make steel, nails, and other common metallic items we see around the house. If you put something made of iron near a magnet, it will cause the electrons to line up, the iron then acts like a magnet. It will have a north and a south pole and attract other magnetic objects.
[ 4 ] We use magnets and electricity to do work. Many of the appliances you are familiar with have some kind of electromagnet inside. An electromagnet is made from copper wire, an iron core, and a source or electricity or current. If you pass current around the iron core, then the core becomes magnetized. If you stop the current, the iron becomes demagnetized. Think of how scrap metal is moved in a junkyard; a large crane with a magnet on the end picks up the metal. When the crane is turned off, the magnet stops working and the metal drops to its new location.
[ 5 ] These types of electromagnets can also power a motor. If you pass current through a coiled wire and place the wire near a magnet, the current can cause the wire to spin. This spinning can then be used to do mechanical work, such as spinning the blades of a fan or turning the wheels of a car. Electromagnets are also used in computer disc drives, speakers, power windows and locks.
[ 6 ] If you ever need a picture of the inside of your body, doctors might order an MRI; MRI stands for Magnetic Resonance Imaging. MR imaging uses a powerful magnet to form a magnetic field. This magnetic field along with the radio waves and a computer work to form detailed pictures of organs, bones and soft tissues. An MRI can be used to diagnose blockages, broken bones, tumors or other abnormalities. Just pay attention when the nurse tells you to take off your jewelry before going into the machine, anything metal can interfere with the machine’s magnet.
[ 7 ] Permanent magnets also have practical uses, such as the magnets hanging on your refrigerator or the magnets used to latch doors. Multi tools use magnets to attach different screwdriver heads to a base. Compasses contain a tiny magnet that aligns to the earth’s magnetic field, so it always points north.
[ 8 ] Credit card and ATM machines contain electromagnets that read the magnetic strip on a credit card. When the card is swiped through the machine, the data are read by the movement of the magnetized spots causing small electrical voltages that read the data on the card. Be careful storing credit cards near other magnets, the strip on the card can become demagnetized and will no longer swipe in those machines.
Analysis: Answer each question and indicate (on the blank) where you can find the answer within the reading. Paragraphs are numbers.
1. Naturally occurring magnets are called: [ P ] = ___ a. compasses b. poles c. electromagnets d. lodestones
2. Which of the following is NOT needed to make an electromagnet? [ P ] = ___ a. copper wire b. electric current c. lodestone d. iron nail
3. The invisible force around every magnet is called the: [ P ] = ___
a. magnetic field b. electromagnet c. compass line d. coil
4. How do you magnetize an iron nail? [ P ] = ___
a. place it near other magnets b. wrap a wire with a current around it c. both of these will magnetize the nail
5. Magnets are named after: [ P ] = ___
a. the place they were first found b. the person who discovered them c. the type of metal found in all magnets
6. Where might a person see an MRI? [ P ] = ___ a. at a junkyard b. in a hospital c. at a nuclear power plant
7. The strip on the back of a credit card contains a: [ P ] = ___ a. computer chip b. a tiny magnet c. a coiled wire
8. The wheels of a motor spin due to the electricity flowing through a wire coil and the coil’s: [ P ] = ___
a. magnetic energy b. potential energy c. heat friction d. attraction to a magnet nearby
9. When electricity stops flowing through an electromagnet, what happens? [ P ] = ___
a. the poles of the magnet switch sides b. the magnet stops working c. the electricity is transferred into the magnet
10. The needle of a compass always points: [ P ] = ___a. north b. south c. east d. west