一长载流导线弯成如右图所示形状，则O点处磁感应强度：
A: 大小为
B: 大小为
C: 方向垂直于纸面向外
D: 方向垂直于纸面向里
A: 大小为
B: 大小为
C: 方向垂直于纸面向外
D: 方向垂直于纸面向里
举一反三
- 若x2+y2=1，则dy为（ ） A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/d045b5f235a54083ab91e6f717cf00d8.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/74173c5355234874ab8cb9275865d5d6.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/bbfb37ba58fc4de0aa8688e0bb53cef5.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/f9a206c25e8c4ea1bd7b51519afd76b7.png" />
- 对于正序的对称三相电源，已知<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/d469ef1a00bf4a7b9f72206db92b2722.png" />则（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/f46f01b8a0944bf5b97b3085df4963af.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/bdc84f660db9480893ab3eb3df8c9174.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/2419acedbbc14be7b11bb6e2cb005039.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/6fabd0d71b0344b68b86a539fd0e0c9e.png" />
- 下列情况中，会产生感应电流的有： A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/1e2e7b8e99294e8a824d5906dda51113.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/6081bc4ae79e452d904680d64f32af5a.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/655e36b2c61547b09b3411739b7ad3be.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/2735a230795a4cbda1a0197612327818.png" />
- 下列函数中不是复合函数的是（ ） A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/852398e68ff74631bd3a10e9b908904b.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/b2421a13aeb94b93b18f4e7a67c2630f.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/f8c9b5fc3bc24e378a5013539240f424.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/78be77e785734fecbef1cc7dec213352.png" />
- 与y=x是同一个函数的是（ ） A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/f86ae5251f654e2883551f545dfe08e7.png"> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/9423178e08ad4e9dbdc9367e98a5ef51.png"> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/cdc5f4144cbb469ab64328415e12a732.png"> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201905/c040b4fc143f484587591e1bb39b7dfc.png">