The Inductive Action of the Earth
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-336
2025-11-29
11
can be shown most strikingly as follows:
Demonstration. - Select a soft iron bar about an inch in diameter and three or four feet long. Holding it horizontally in an east and west line, present its ends successively to the N and S ends of a magnetic needle. Both ends will attract each end of the needle, showing that the bar is not polarized.
Next hold it in the line of dip, with the lower end at the side of the needle and near the north end. The needle will be repelled at once, showing that in this position the bar is polarized. Reverse the bar and make the same test with the needle, and the needle will show that the polarity of the bar is reversed. Bring the bar into the first horizontal position and again it will attract both ends of the needle, showing that it is not polarized. Place the bar again in the line of dip and give it one or two sharp blows with a hammer. Now place it in the first horizontal position; and on testing it with the needle it is found to be polarized. Hold it horizontally in an east and west line and give it a few sharp blows; and it will be found to be not polarized.
With the magnetized sewing needle, test the steel or iron rods about the building for polarity. Most of them will be found polarized, especially if they have been in a vertical position. .....
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