Self-induction
المؤلف:
GEORGE A. HOADLEY
المصدر:
ESSENTIALS OF PHYSICS
الجزء والصفحة:
p-398
2025-12-13
23
We have just seen that a change in the current in one coil induces a current in a second coil near the first. It is evident that a change of current in one turn of a coil should also induce currents in adjacent turns of the same coil. This effect is called self-induction, and its existence can be shown as follows:
Demonstration. - Couple a battery, switch, galvanometer, and coil as shown in Fig. 1. Turn on the current, and observe the direction of the deflection. Bring the needle back to zero, and keep it there by placing a cork at one side to stop it. Break the current, and notice that there is a throw of the galvanometer in the opposite direction, showing that the current induced in the coil is in the same direction as the current sent by the battery.
Let Fig. 2 represent five turns of wire surrounding an iron core, carrying current away from the observer in 1, 2, 3, 4, 5, and toward the observer in 1', 2', 3', 4', 5', as indicated.
To understand the reason for self-induction let us assume that the current is just beginning, and is increasing in intensity. Let us consider the effect of the lines of force set up around turn No. 3 by the current passing through it. As the current increases in strength the lines of force expand from wire No. 3 as a center, and pass through the iron core and around the outside of the wire. As they increase in diameter they cut across conductors 2 and 1 to the left, and conductors 4 and 5 to the right. By applying the rule for the direction of induced currents, we see that in all these conductors the induced current is in a direction opposite to the current already passing in the coil. When the current in the coil is broken, the lines of force contract to the conductor that produced them; they cut the other turns in the opposite direction, so the induced current is reversed and in the same direction as the current in the coil. The same reasoning applies to every turn of the coil. This means that when the current is broken, the lines of force belonging to every turn of the coil cut every other turn in the coil, and the result is a self-induced current of considerable strength.
الاكثر قراءة في الكهرومغناطيسية
اخر الاخبار
اخبار العتبة العباسية المقدسة
