在如图所示的电路中，电源电动势为E.内电阻为r、R 1、R 2为定值电阻，当滑动变阻器R 3的滑动片P由a向b移动时 (  )  

试卷相关题目

SQL Error: select id,body,options from ***_enewstiku_ where sourceid='15670' and id < 1311427 and id<>'1311427' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='15670' and id > 1311427 and id<>'1311427' order by id asc limit 5