Magnetic Properties of the Solenoid
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
P-365
2025-12-09
30
A solenoid is formed of a coil of insulated wire wound in the form of a cylinder in one or more layers.
Demonstration. - Place upon a table a magnetic needle, and let it come to rest.
Place a solenoid S with one end about two inches from the north pole of the needle. Close the key K, sending the current through the solenoid, and the needle will be acted on at once, being either attracted or repelled according to the direction of the current in the coil.
The length of a solenoid is usually great compared with its diameter, but its magnetic properties are still retained even if it is shortened to a single turn. Figure 345 shows lines of force of such a turn.
An important use is made of the solenoid, in the circuit breaker which is used to protect electrical circuits from too heavy currents. Figure 346 gives, in diagram, the path of the current. When the current in the solenoid becomes too great, the iron plunger P is drawn up,
strikes the brass pin p, which trips the catch C, that holds the arm A in place. The spring S, which is compressed when the breaker is closed by the handle H, pushes A out and breaks the contact between A and B. The amount of current required to pull up the plunger P depends upon its position, which is regulated by the thumbscrew T.
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