题目

频率为50Hz的交变电流,其电压u=120sinωt                V,把它加在激发电压、熄灭电压均为84V的霓虹灯的两端,则在半个周期内霓虹灯点亮的时间为                                         .(=1.4)                                                                                                                                                                   答案:s                                                                                                                                        
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