单项选择题
已知正弦交流电u=311sin(314t+30°)V,该电压第一次达到311V,需要的时间是()。
A.1/30s
B.1/60s
C.1/300s
D.1/600s
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单项选择题
A.1/30s
B.1/60s
C.1/300s
D.1/600s
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