题目

如图所示，理想变压器的输出端接有一电动机，电动机的电阻为R，电动机带动一质量为m的重物以速度v匀速上升．设变压器的输入功率为P，原、副线圈匝数比为n1：n2，电动机因摩擦造成的能量损失不计．则图中电流表的读数应为                                                                                ．                                                        答案：                                                                                                                                                                                                                                                                                                                                                                                                                       

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