两根长度相同的细导线分别多层密绕在半径为R 和r 的两个长直圆筒上形成两个螺线管，两个螺线管的长度相同，R ＝2r，螺线管通过的电流相同为I，螺线管中的磁感强度大小BR 、Br满足( )
A:
B:
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D:
A:
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举一反三
- 拉普拉斯（Laplace）方程的表达式为（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/26731bcad75f41389448b29292940653.jpg" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/40e7e55a72ee44f59b45d20c84ebe3a6.jpg" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/c65a79ea4d754174b99f34020d6e1735.jpg" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/139e8d3dc37941549e7b6b1731243172.jpg" />
- 质点作半径为R的变速圆周运动时的加速度大小为（v表示任一时刻质点的速率）( ) A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/566625ddf2c44d81babb2fdd6c1215b2.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/bceb93f381844a3988a0291fea01e102.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/e43ab8d2b7b4422a9088f99e594718cb.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/b1a89995aed242d9b12b93495a7ebdae.png" />
- 平面一维稳定渗流的压力分布公式为（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/d08348f3b84f442d87994311dc13686b.jpg" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/2df214c86c5e4103897ba81ce2c6cd98.jpg" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/cc98e4a778cc463c965ac8115e028f86.jpg" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/bc82177c19d44acfa1b365c3d66ed0a4.jpg" />
- 下列四种产品中，（）属于主体附加。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/7de8bb1790ee4eccbc8fe23d663cb293.JPG" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/9f76d9ce04cb4729b4739bdd64d5917b.JPG" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/b4d8b1ab0b9c4f5e8d165f7afd487e00.JPG" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/4862f4e33e114c63bcfa3ebf5c112cba.JPG" />
- 下列四种产品中，（）属于同类组合。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/ee5cc627e4a243ea8fc5025d6736de65.JPG" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/95326815255349e7bb11324655294818.JPG" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/07ebf5a3e62b47d2be75f2574f2bee3e.JPG" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/a46447046f5340d8977c1ffed9a70772.JPG" />