The Magnetic Needle
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-302
2025-11-26
53
is a small bar magnet suspended by a thread or balanced upon a pivot (Fig. 1). It is used in many instruments, as in the compass. If we should continuously follow the direction in which it points, our path would be a magnetic meridian; and that spot in the Arctic regions where all magnetic meridians meet is called the north magnetic pole.
FIG.1
Demonstrations. - Magnetize a sewing needle by drawing it across the ends of a bar magnet. Begin the stroke at the middle of the needle and end it at the point, drawing it across the + end of the magnet. Do these ten or twelve times. Reverse the. needle and draw it across the - end of the magnet, beginning at the middle of the needle and ending at the eye. Unravel a fine silk thread, and tie a single strand around the middle of the needle. When you have balanced the needle so that it will hang horizontally, fasten the thread in place by a bit of beeswax or sealing wax, and you have a magnetic needle that will serve for many experiments. Suspend the needle and find the magnetic meridian. Observe which end of the needle points north, and notice whether or not it is the end that was drawn over the north end of the magnet.
end that was drawn over the north end of the magnet. Make a small bar magnet out of a good-sized knitting needle. In stroking it with the magnet, lay it upon a piece of board and stroke it with the + end from the middle to one end of the needle. Reverse the needle and magnet and repeat. In order to make a strong magnet, the stee must be stroked a great many times. Test it with iron filings and nails.
FIG. 2 - Magnetic Meridians
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