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單項選擇題

已知R、L串聯負載R=40Ω，L=95.5mH，通有頻率f=50HZ的交流電，則此負載功率因數為（）。

A.0.5
B.0.6
C.0.75
D.0.8

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一閉合導線回路產生感應電動勢的大小取決于回路的（）

A.磁通量大小
B.磁通改變量多少
C.磁通變化率大小
D.磁通密度大小

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交流電機和變壓器等設備選用硅鋼做鐵心材料，目的是為了（）。

A.減少渦流
B.減少磁滯損耗
C.既減少渦流又減少磁滯損
D.增加設備絕緣性能

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