If there are no field lines, there is no force, and the result is magnetic shielding. Magnets have field lines that exert a force on magnets or iron. Our Snack, Magnetic Lines of Force, demonstrates this phenomenon.įield lines come from the north pole of a magnet and return to the south pole.
By sprinkling iron filings on a piece of paper placed on top of a magnet (or a couple of magnets), you can see the field lines. Iron filings also line up along field lines. A compass lines up along a field line, so you can trace field lines with a compass. Scientists model magnetic forces using field lines. If small compasses are used to map the magnetic field around a bar magnet, they will point in the directions shown: away from the north pole of the magnet, toward the south pole of the magnet. The paper clips will drop off when the field lines interact with the closed scissors. Magnetic field lines are defined to have the direction that a small compass points when placed at a location. Insert an open pair of steel scissors between the pieces of cardboard, then close the scissors as if cutting the field lines. With the Earth's north-south magnetic force, these lines fan out from the vicinity of the south magnetic pole, arch above the (magnetic) equator and converge again in the region around the northern magnetic pole. How could you modify the sandwich to make a weaker magnet work better? He named them magnetic lines of force, though nowadays 'magnetic field lines' is the usual term. As the magnetic field strength gets weaker, it gets harder to keep the paper clips from falling. Black sand from the beach-which is made of magnetite and does not rust-can also be used as a substitute for iron filings.Try using only one or two magnets. To prevent the bottle’s collapse, simply punch a small hole in the plastic with a pushpin. As the iron rusts, it combines with and removes oxygen from the air trapped in the bottle. This happens because the iron filings will begin to rust. Note that if you’ve sealed the plastic bottle really well by jamming the test tube into its mouth, the sides of the bottle will begin to collapse inward after a few hours-particularly if the inside of the bottle is damp.
Even so, this Snack gives an indication of the shape of the magnetic field in three dimensions. The iron filings stick out like a crew cut on the ends of the magnet but lie flat on the sides (click to enlarge diagram below).īecause the iron filings become magnets themselves, their presence slightly changes the shape of the magnetic field. The field of a cylindrical magnet comes out of the end of the magnet and then loops around next to the side. Since iron filings are rod-shaped, the atoms line up pointing along the length of the rod, and the rods line up parallel to the direction of the applied magnetic field. In a rod-shaped piece of iron, the atoms will tend to line up so that all the north poles face one end of the rod and all the south poles face the other end. Because the iron atoms line up, the piece of iron becomes a magnet and is attracted to the original magnet. When you bring a magnet near a piece of iron, the iron-atom magnets line up with the applied magnetic field: The north poles of the iron atoms all point in the same direction. Most pieces of iron are not magnetic, because the atomic magnets all point in different directions.
Each atom in a piece of iron is a magnet, with a north pole and a south pole.
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