Parallel Currents
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
P-394
2025-12-13
11
Demonstration. - Wind a spiral 3 cm. in diameter, of about thirty turns of No. 24 insulated copper wire. Suspend it from a rod and couple the upper end to the + pole of a battery. Straighten out a short piece of the lower end of the coil and let it dip into a drop of mercury which is connected with the - pole of the battery.
When the current is turned on, the spiral will shorten and lift the end from the mercury. A spark will pass, then the spiral will lengthen, the point will again touch the mercury, and the action will be repeated.
This demonstration shows, in a simple way, one result of the mutual action of parallel currents. Experiment A B has proved the truth of the following law
- Parallel currents flowing in the same direction attract each other, and those flowing in opposite directions repel each other.
It will be observed that this law is directly opposite in form to the statement of the fundamental law that lines of magnetic force going in the same direction repel each other. That the two laws are statements of the same phenomena, however, can be shown by a consideration of Figs. 2, 3, 4.
In the case of A and B, which are carrying currents in the same direction (toward the observer), the lines of force between the wires are going in opposite directions. This means that the lines of force will run into each other and, by shortening, tend to bring the wires together, with the lines of force inclosing both, as in Fig. 3.
In conductors C and D, in which the currents are moving in opposite directions, the lines of force between the wires are in the same direction, and repulsion is the result. Among the many ways of t showing this tendency of the lines of force to contract and move the conductor is the following:
Demonstration. Suspend a coil of loosely wound insulated copper wire over a horizontal glass tube as shown in Fig. 5. On sending a current through the coil the wires will move together, Fig. 6. An iron rod placed in the tube will bring the wires together more quickly.
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