题目

Listen and write down the sentences. 答案:【1】It was typical of her to forget.如图所示,R1为定值电阻,R2为可变电阻,E为电源电动势,r为电源内电阻,以下说法中正确的是(  )A.当R2=R1+r时,R2获得最大功率B.当R1=R2+r时,R1获得最大功率C.当R2=0时,R1上获得最大功率D.当R2=0时,电源的输出功率最大
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