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The Electromagnet

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  P-366

2025-12-09

476

If the solenoid is provided with a soft iron core, it becomes an electromagnet. Since the iron offers a better path for the lines of magnetic force than air, that is, a path having less resistance, the introduction of the iron increases the number of lines of force (maxwells) that a certain current will generate on passing through the coil. This means that the magnetic strength of the electromagnet is increased. 

Demonstrations. - Make an electromagnet by winding several layers of insulated copper wire No. 16 around a wooden spool about a foot long, and putting a piece of gas pipe or soft iron rod inside the spool for a core. Couple with several cells of a battery, and when the current is turned on, dip the end of the core into a box of nails; lift the magnet and note the effect as shown in Fig. 1. Break the current. What is the result? Support the same magnet vertically, and lay over the upper end a sheet of glass (Fig. 2) upon the under side of which a sheet of paper has been pasted. Sift over the plate an even layer of iron filings, and, tapping the plate lightly, turn on the current. The lines of force will be shown in a striking manner.