电流由长直导线1沿半径方向经a点流入一电阻均匀的圆环，再由b点沿切向从圆环流出，经长导线2返回电源(如图)。已知直导线上电流强度为I，圆环的半径为R，且a、b与圆心O三点在同一直线上。设直电流1、2及圆环电流分别在O点产生的磁感强度为 、 及 ，则O点的磁感强度的大小http://image.zhihuishu.com/zhs/onlineexam/ueditor/201902/81d4b4af3f4546fb86761070f85a65f1.PNG

电流I由长直导线1沿垂直bc边方向经a点流入由电阻均匀的导线构成的正三角形线框，再由b点流出，经长直导线2沿cb延长线方向返回电源(如图)．若载流直导线1、2和三角形框中的电流在框中心O点产生的磁感强度分别用、和表示，则O点的磁感强度大小 （）https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/3d85b100e94e4d689c52

ZHDY6-2*如图所示，两根导线沿半径方向引向铁环上的A，B两点，并在很远处与电源相连。已知圆环的粗细均匀，电流I，圆环半径R，θ=60°。则环中心O的磁感应强度为（）http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/8eb471626f954ed7a2c0f1cf1e017fde.png

无限长直导线在P处弯成半径为 R 的圆，当通以电流I时，则在圆心O点的磁感强度大小等于（ ）。<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/ea9d82a600684de2a916e5c304869893.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/ba82b51586c84ba098c3a6464b629ffa.png" /> B: 0 C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5ed485ce1868458ca1d09cb5e134c4d0.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/07acf7ef8e7f4393864785943a134038.png" />

图示有侧移结构，设横梁的水平侧移为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201904/5b1b0d2260734afd9d372476eccd0a52.png"/>，计算约束状态下杆件的固端弯矩，正确的是（ ）<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201904/0bb431e37a424b1f841ad9350d80f241.png"/> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201904/ef65ff72dc6b4179bee92ce4ff148aad.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201904/5ca987b52284485a986cb954a09b51a0.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201904/0c7f5a6de2714ac0bbb5a243d9b8da4b.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201904/94aab58ed2f94f90af7c4ea00aecf764.png"/>