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在“自感”知识教学中,演示断路自感现象通常都采用图1所示装置。断开开关K,小灯泡 S 发出明亮的一闪后才熄灭,以此说明自感现象。可是在教学实践中发现,不少的人对断路自感实验存在着一些似是而非的错误认识,而且这些错识具有一定的普遍性、代表性和迷惑性,以下对其一一进行剖析。典型佯缪之一:断开电源开关、灯泡明亮的一闪后才熄灭是因为断电瞬间线圈中的电流突然增大了。剖析:断开电源开关 K,线圈中产生的自感电动势大小为ε_L=(r+B)/rε·e~(-(R+r)/L·t)(R 为灯泡的电阻,L 为自感系数,r 为线圈的内阻,ε为电源电动势,其内阻忽略不计)。可见,断开 K的瞬间线圈两端的自感电动势
In the teaching of “self-inductance” knowledge, the demonstration of disconnection self-induction phenomenon usually adopts the device shown in FIG. Turn off the switch K and the light bulb S goes out after a bright flash to show self-induction. However, in the teaching practice, it is found that many people have some erroneous misperceptions about the circuit-breaking self-inductance experiments, and these misunderstandings have certain universality, representativeness, and delusion, and they are analyzed one by one. One of the typical features is that when the power switch is turned off, the light bulb is extinguished after a bright flash, because the current in the coil suddenly increases when the power is turned off. Analysis: disconnect the power switch K, the self-induced electromotive force generated in the coil is ε_L = (r + B) / r ε · e ~ (- (R + r) / L t) (R is the resistance of the lamp, L is Self-inductance coefficient, r is the internal resistance of the coil, ε is the electromotive force of the coil, and its internal resistance is ignored.) It can be seen that the self-induction electromotive force at both ends of the instant coil of K is disconnected.