Just to share some idea... I think the most fundamental assumption of using KCL and KVL is... you are using abstract concept to describe things. The beauty of EE is that we can use abstract V-I so well instead of direct dealing with E-M...so well that we all feel V-I is the real quantity, and embeded them into our everyday live. E-M is from Physics department but we have our own way to live with it. This V-I concept happened to work with the "pattern recognition" technique. By "pattern recognition" I mean the topology. Top line is VDD. Bottom line is ground. Left is input. And right is output. We borrow the concept of topology from Math department, do some modification and apply to our EE world. With the two weapons in hand, we can put complex calculation away and start to "model" things. However, there's always limitation that our method won't work anymore. Berkeley SPICE was developed to help us calculate complex circuit, but still, they can only do V-I and topology. It's just that... over time we get used to "back of the envelope" calculation (and SPICE.) So we figure out some other way to "model" something that's not supposed to work with V-I (instead, they should work with E-M). Probably it's our nature, if the model fit data at certain range under certain environment, we are happy. So if you are claiming KCL and KVL will work as long as there's model for it, this arguement is kind of loose, don't you think? It works because we let it be that way, not because it works by itself. ※ 引述《cpt (post blue)》之铭言： : ※ 引述《sexyman (现在新歌没好听的)》之铭言： : : 这个板友，如果你是念电机系，我想你的电磁学从大学修过课後 : : 就从来就没有用过了，因为你的推导与观念完全是错误的 : 我想做的只是提供一个我觉得合理的思考方式 : 这当然和严谨的推导不同 : epsilon0 和 mu0 是物理常数 : 把它们设为零, 就好像把光速设为无限大一样 : 在适当的尺度下, 这样的假设是合理的, 我并没有要做过多的延伸 : 但是把 epsilon0 或 mu0 设为零, 在根本上当然与事实不符 : 这也就是为什麽 KCL/KVL 在根本上也是与事实不符 : 只不过这个误差在大部分情况之下可以忽略 : : 第一点是你一直强调要假设 epsilon0 与 mu0 为零的观念为错误 : : epsilon0 与mu0 是一个物理常数，是不容许你假设为零的 : : 如果你这一点原则都无法柄持，你也不必浪费你的时间去做以下的推导 : : 因为你的推导根本就是在一个错误的假设上 : : 第二点是你的证明用错误的方法去简化不必简化的东西 : : 比方说，由 curl(E) 的公式得到 KVL，不是因为 mu0 = 0 : : 而是因为没有时变磁场而造成的；如果有时变磁场的话 : : KVL 仍然成立，那个时变磁场所造成的积分量叫做「电感」 : KVL 之所以成立, 是因为我们额外去 model 了这个"电感" : 但事实上电感无所不在, 如果有任何一小段没有 model 进去 : KVL 就无法反映实际的物理现象 : 因此, 与其说是"没有时变磁场", 为什麽不能想成"忽略时变磁场"呢? : 这跟把 mu0 设成 0 不是一样的意思吗? : (这不是在反驳你, 我是真的想知道为什麽这样不对) --

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