推荐回答（2个）
原副线圈看似是互相分离的 实际上是通过相同的磁感线连接在一起的 由于变压器是理想的 那么可以这样设想 当原线圈的的电流加大时 假设没有副线圈 那么由于原线圈家的的磁场 会导致 原线圈产生感抗 理想变压器由于线圈本身没有电阻 而且没有磁损 所以 可以看作是原线圈的感抗无限大 那么 原电路由于无限大的感抗 所以导致了原电路中的电流时零
但是
如果有副线圈的话 那么当原线圈中的磁感应强度加大时 副线圈会出现感应电流 这种感应电流是由于副线圈产生了与原线圈磁场变化相反的磁场所产生的 所以 这个磁场变化会导致 原线圈的感抗变小 所以导致了 原电路中 产生了感应电流 而且 副电路得电阻越小 而电压一定所以 导致了副线圈的磁感应场对原线圈的阻碍作用越小 所以 原线圈的感抗就变小了 所以 电流加大 功率加大
第二个题 可以从第一个题中得到解答 因为 副线圈不存在是 原线圈的感抗 是正无穷 所以 没有 电流
其实这是电磁感应的基本原理。当闭合线圈切割了磁力线时，在线圈里就产生了电流，如果不是闭合线圈，那在线圈的两端就有电压。以上就是发电机原理。在变压器原理中当原边通入交变得电流时，在铁心磁路中产生了交变的磁通（其频率与交变电流的相同），在副边线圈中感应了交变电压。这是与发电机原理相同（切割磁力线引起的）。如果你在原边线圈中通的不是交流，而是直流，在铁心和副边线圈中就不会有磁通或电压感应出来（当然在接通和断开的瞬间会产生）。这就是变压器的电磁感应定理。
当变压器原边加了交流电压后，（实际上这时有励磁电流）在铁心中建立起交变的磁场。在副边中就感应出交流电压，此时就叫空载电压。当有负载时，副边线圈中有了负载电流，在原边线圈中，在励磁电流的基础上按原副边匝数比增加了电流。此时变压器就是这个负载的电源。
当原边施加交流电压时，副边感应出交流电压，反过来在原边线圈中建立起与外施电压相反的反电势。这就回答了第二个问题。反电势的概念在电动机中很容易理解。如果没有反电势（强迫电机不转），电机就会烧毁。这就像作用力与反作用力的概念一样。
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