某電阻R=100W ,在電阻兩端加交流電壓。則電阻消耗的功率為()W.
A.2000 B.200 C.484 D.1100
A.20000 B.2000 C.10000
如圖D-3所示,若U=140V,R1=10W ,R2=25W ,則電路的總電阻R為()W.
A.15 B.30 C.50 D.35