变压器是一种用来改变交流电的电压和电流的电气装备。在中学只研究单相理想变压器,它应符合如下三个条件:(1)原、副线圈的电阻极小(r_1＝r_2≈0),变压器内部能量损耗(铜耗、铁耗)忽略不计,即认为它的输出功率和输入功率相等。(2)原、副线圈中交变电流所产生的磁通量都通过了铁心,没有从线圈匝间漏掉,即认为通过原、副线圈的交变磁通量相同。(3)当副线圈开路时,原线圈因自感系数L很大,故它 A transformer is an electrical device that changes the voltage and current of an alternating current. In the middle school, only the single-phase ideal transformer is studied. It should meet the following three conditions: (1) The resistances of the primary and secondary coils are very small (r_1=r_2≈0). The internal energy loss (copper and iron loss) of the transformer is negligible. That is, its output power and input power are equal. (2) The magnetic flux generated by the alternating current in the primary and secondary coils passes through the iron core and does not leak from the turns of the coil, that is, the alternating magnetic flux passing through the primary and secondary coils is the same. (3) When the secondary coil is open, the primary coil has a large self-inductance coefficient L, so it is