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[单选题]
某一交流电的数学表达式为u=220sin(120πt+30°),该交流电的频率为()Hz。
A.50
B.30
C.120
D.60
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A.50
B.30
C.120
D.60
A.u=380sin(100t+180°)V
B.u=311sin(200πt+180°)V
C.u=220sin(628t+180°)V
D.u=-311sin100πtV
A.电流滞后电压40º
B.电流滞后电压30º
C.电压超前电流50º
D.电流超前电压30º
电压和电流的瞬时值表达式分别为u=220sin(ωt-10°)和i=5sin(ωt-40°),那么()。
A.电流滞后电压40°
B.电流滞后电压30°
C.电压超前电流50°
D.电压超前电流30°
A.i1=2sin(314t-150°)A
B.i2=3sin(314t-90°)A
C.13=4sin(314t+75°)A
D.i2=3sin(314t-30°)A
A.u=20sin(50t+30°)V
B.u=20sin(314t+30°)V
C.u=28.28sin(50t+30°)V
D.u=28.28sin(314t+30°)V