如图所示，理想变压器原、副线圈匝数之比为n1∶n2＝4∶1，交流电源的电动势瞬时值e＝220
sin(100πt) V，副线圈接一个R＝55Ω的负载电阻。下列结论正确的是
A．副线圈中电压表的读数为55V
B．副线圈中输出交流电的周期为
s
C．原线圈中电流表的读数为0.25A
D．原线圈的输入功率为55W
CD
题目分析：由瞬时值的表达式可知，原线圈的电压最大值为
，所以原线圈的电压的有效值为
，在根据电压与匝数成正比可知，副线圈的电压的有效值为55V，即为电压表的读数，所以A错误；
变压器不会改变电流的周期，电流的周期为
，所以B错误．
副线圈的电流为
，根据电流与匝数成反比可得，原线圈的电流大小为
，所以C正确．
变压器的输入功率和输出功率相等，副线圈的功率为
所以原线圈中的输入功率也为55W，故D正确；
故选CD
点评：掌握住理想变压器的电压、电流之间的关系，最大值和有效值之间的关系即可解决本题．
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