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ELECTRICAL ACTION 23
which is to place a piece of iron close to a piece of magnetic ore. The iron becomes magnetized by virtue of the fact that it has been placed in a magnetic "field. " It loses its magnetic power when it is removed from the field. A piece of steel is more difficult to magnetize than a similar piece of iron, but when removed from the field it remains a magnet. It can be used to magnetize other pieces or iron or steel, just as the original ore was.
(57) Iron and steel can also be magnetized by placing them close to an electrical conductor carrying direct current. Steel magnets are manufactured by placing them inside a coil of wire carrying direct current. Projectionists often magnetize steel screwdrivers and other tools by winding some turns of soft, insulated wire around the tool and connecting the ends of the wire with a battery or other source of d.c. The magnetized screwdriver or hammer are useful because they attract small iron screws, bolts, etc., preventing such objects from becoming lost.
(58) The wire carrying current acts in the same way as the magnetic ore or magnetized steel, both in magnetizing iron and steel objects brought within its field and in attracting small, light pieces of those metals. In short, a wire carrying current is a magnet — an electro-magnet — as long as the current continues to flow. It attracts the needle of the magnetic compass, and in other ways acts like a magnet made of steel or iron.
(59) The power of an electro-magnet can be increased by bunching a long length of wire in a small area; this is done by winding the wire in the form of a coil. The magnetic force can also be increased by increasing the amperage in the wire. Hence, electro-magnets are sometimes rated in "ampere-turns," that is, the amperage flowing multiplied by the number of turns of wire in the coil.
(60) The magnetic force, which acts upon objects located at some distance from the magnet, is called a flux, and conveniently measured in terms of "lines