圆形电流的半径为r，电流为I，则圆心处的磁感应强度为
A:
,垂直纸面向内
B:
,垂直纸面向外
C:
,垂直纸面向内
D: 0
A:
,垂直纸面向内 B:
,垂直纸面向外C:
,垂直纸面向内 D: 0
举一反三
- 如图所示电路的逻辑表达式F=（ ）。<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/8655693a417e4e43a32e0732ed533c96.png" /> A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/beda73211aea49f082d9137fd4eb0526.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/7388c99ee0824f20bcf85893934a2f6a.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/9a5c81e78b344c79a9389e932a7f55ce.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/82193a9a030243728012b02e15718987.png" />
- 某反应在标准态和等温等压条件下，在任何温度都能自发进行的条件是（ ）。 A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/63c6a7b5b3114c1095cb68d96ebd27ec.png" />< 0，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/d11dd437fcbe440d886e25a9a04f2c0e.png" />> 0 B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/63c6a7b5b3114c1095cb68d96ebd27ec.png" />> 0，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/d11dd437fcbe440d886e25a9a04f2c0e.png" />> 0 C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/63c6a7b5b3114c1095cb68d96ebd27ec.png" />> 0，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/d11dd437fcbe440d886e25a9a04f2c0e.png" />< 0 D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/63c6a7b5b3114c1095cb68d96ebd27ec.png" />< 0，<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/d11dd437fcbe440d886e25a9a04f2c0e.png" />< 0
- 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="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/247132caa86643248801a9ce73153643.png" /> A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/d6ca935b43b5409982580c397b20452a.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/05df5ede8d854c86adb4aa49ab7d213a.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/fd586a02dd0d48d2a9d8451722bd0cc8.png" /> D: 0 E: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/5b15cee769754f5b8d999d9c5bb28961.png" />
- 体系处于<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/7bae90aad0f0442d9d6adf4ff4c69c2c.png" />状态,则体系的动量取值为 A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/156065cb1de5431a9a2ea0b029f26f79.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/627120343f054317828addfe01200e5b.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/09f88938fc6f43a0819284117c0b14fa.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/2311487532fb45c789f7dce939291db1.png" />
- 如图示并联管路，已知各支路的沿程阻力系数之比为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/6e209020d20f4543823ce6516ae8ca06.png" />，管长之比为<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/50814fe028094040bc955d8e1542b6d2.png" />，且<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/40b4c6a9565b483590c5c7d607e7ed66.png" />，则两支管的流量之比<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/1055534bfce6426a94682ba086a5b17e.png" />=（）。<img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/77815369f5cd41f3a2e68b9524b454c5.png" /> A: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/0cd231eebe45465f941a0f614743e6d2.png" /> B: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/7555afa5223e40bf89ca575cf7b52754.png" /> C: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/1b06cd474b844644a6d97ad87d208e94.png" /> D: <img src="https://image.zhihuishu.com/zhs/onlineexam/ueditor/201909/d0b2bca045414236a7d1c9925a9264f2.png" />