题干

一理想变压器原、副线圈的匝数比为n1n2=1∶2,电源电压u=220sinωt(V),原线圈电路中接入一熔断电流I0=1 A的保险丝,副线圈中接入可变电阻R,如图4-2-14所示,为了使保险丝不致熔断,调节R时,其阻值最低不能小于(  )

图4-2-14

A:440 Ω

B:440Ω

C:880 Ω

D:880Ω

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C

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