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20.Mark your answer on your answer sheet.
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52. 一交流電源供給一電感性負載用電,測得有效功率 500W 與無效功率 500VAR,則其功率因數為 (A)0.707 領先 (B)0.5 落後 (C)0.707 落後 (D)0.5領先 。
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53. 3ψ4W11,400 伏特高壓用戶,其負載為 1,200kW 功率因數為 0.8,欲將功率因數提高至 1,則需增加之電容器容量為 (A)600 kVAR (B)700 kVAR (C)800
54. 3ψ4W 11.4kV 線路負載電流 50A 時,消耗功率為 800kW,則其功率因數為 (A)91% (B)81% (C)71% (D)61% 。
55. 純電容性負載之特性為 (A)電流超前電壓相位 90°(B)電壓超前電流相位 90° (C)電流與電壓同相位(D)電壓超前電流相位 30° 。
56. 某線圈接入直流 100 伏特電壓時,通過電流為 25 安培,接入 100 伏特交流電壓時,電流為 20安培,此線圈之感抗為 (A)1Ω (B)2Ω (C)3Ω (D)4Ω 。
57. 一線圈之電阻為 30Ω,在電源頻率為 50Hz時,總阻抗為 50Ω,當電源頻率調為 200Hz時,該線圈電之感抗為 (A)100Ω (B)120Ω (C)140Ω (D)160Ω 。
58. 一 RL 串聯電路,電阻 R=4Ω,感抗 XL=3Ω,下列敘述何者正確? (A)總阻抗為 7Ω (B)電壓滯後電流 53 度 (C)電壓超前電流 53 度 (D)總阻抗為 5Ω 。
59. 一 RL 串聯電路,電源 v(t)=100 sin377t、電阻R=10Ω、電流 i=5A,該電路之總阻抗為多少歐姆? (A)20∠0° (B)20∠30° (C)20∠45° (D)20∠
60. 下圖係 (A)LC 串聯電路電流與頻率關係曲線圖 (B)LC 並聯電路電流與頻率關係曲線圖 (C)RLC 串聯電路電流與頻率關係曲線圖 (D)RLC 並聯電路電流與頻率關係曲線圖。
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