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Mutual Action of Magnets

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-303

2025-11-26

522

Demonstration.   Bring the + end of a bar magnet near the + end of a magnetic needle and note the result. Bring the - end of the magnet near the + end of the needle and observe. Make the same experiment on the - end of the needle.

The results of the above demonstration may be stated in the following terms: Like poles repel and unlike poles attract each other. This law is a fundamental one in magnetism and should be made very familiar. The force of the repulsion or the attraction varies directly as the magnetic strength of the poles and inversely as the square of the distance between them.

FIG.1

Demonstrations. - Lay a horseshoe magnet upon a table. Pass a light thread through the eye of a magnetized sewing needle, and by careful manipulation it can be brought to remain in a horizontal position over the ends of the magnet, as in Fig. 276, although only slightly supported at one end. Explain.

FIG.2

Magnetize a number of sewing needles so that their eyes will be south poles and their points north. Thrust them through small corks, leaving the eye half an inch above. Float three of them in a glass of water. Notice their positions, and explain. Now bring the south pole of a bar magnet vertically down over the middle of the glass. Explain the result. Reverse the magnet and repeat. Explain. Increase the number of needles and repeat. These are called Mayer's floating magnets.