【单选题】【消耗次数：1】
一台三相异步电动机的磁极对数p=2，电源频率为50Hz，电动机转速n=1440r/min，其转差率s为( )。
①
1%
②
2%
③
3%
④
4%
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【简答题】
两台三相异步电动机的电源频率为50Hz，额定转速分别为1440r/min和2910r/min，则它们的磁极数分别是多少？额定转差率分别是多少？
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一台三相异步电动机，定子旋转磁场磁极对数为2，若定子电流频率为100Hz，其同步转速为（ ）。
①
1200r/min
②
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