The waters of the lake were so ______ that it looked like glass. A. silent B. calm C. still D. quiet 答案:Bcalm主要指自然界,如天气、海等毫无骚动,风平浪静。
如图所示,两根平行放置的长直导线a和b载有大小相同、方向相反的电流,a受到的磁场力大小为F1,当加入一与导线所在平面垂直的匀强磁场后,a受到的磁场力大小变为F2,则此时b受到的磁场力大小变为
A.F2
B.F1-F2
C.F1+F2
D.2F1-F2