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1 單相變壓器的負載實驗,經由示波器所測得變壓器二次側的負載端電壓與電流波形分別為v(t)=141.4sin(377t)V與i(t)=7.07sin(377t-30°)A,試問負載的虛功率為多少? 91 統測
A 1000var
B 750var
C 500var
D 250var

v有效值=141.4 / 2=100V

i有效值=7.07 / 2=5A

V與I相差30°

Q =VIsinθ=100×5×sin30°=250var