题目

— You shouldn't have gone there alone last night.— But I ______, because Xiao Wang went there, too. A . didn't B . had to C . did D . should 答案：A如下图甲所示，理想变压器原、副线圈的匝数比为4：1，电压表和电流表均为理想电表，原线圈接如图乙所示的正弦交流电，图中R1为热敏电阻（温度升高电阻减小），R为定值电阻。下列说法正确的是：A．副线圈两端电压的瞬时值表达式为 VB．t＝0.02s时电压表V2的示数为12VC．变压器原、副线圈中的电流之比和输入、输出功率之比均为1：4D．R1处温度升高时，电流表的示数变大，电压表V2的示数不变