单项选择。
My ______ long and blond. [ ]
A. hairs are
B. hair are
C. hair is
D. hairs is
答案:C
如图所示,匀强磁场的磁感应强度B=0.1T,金属棒AD长0.4m,与框架宽度相同,电阻r=1/3Ω,框架电阻不计,电阻R1=2Ω,R2=1Ω。当金属棒以5m/s速度匀速向右运动时,求:
(1)流过金属棒的感应电流为多大?
(2)若图中电容器C为0.3μF,则电容器中储存多少电荷量?
焊接应力是怎样产生的?