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（ ）。
A:
B: 0
C:
D:
A:
B: 0
C:
D:
举一反三
- 一定量的理想气体，在温度不变的条件下，当压强降低时，分子的平均碰撞频率<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />和平均自由程<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />的变化情况是（ ）： A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />和<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />都减小． B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />减小而<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />增大． C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />和<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />都增大． D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5499a59dc3754bfdbf231e19c5e2edb9.png" />增大而<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/bba421d6506c4072b583fd4e63b5df81.png" />减小．
- 在电感元件的交流电路中，已知<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/a818ffec501541eaacdc3fd4b3458bfa.png" />，则（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/70961d125a8a493cbdbd3169e8655336.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/65f4ae24f45041548b04d5bb8c113767.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/20d9ff741d534721b621dfe04fb3b2bd.png" />
- 理想气体卡诺循环过程的两条绝热线下的面积大小（图中阴影部分）分别为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/64280a32f9a4401f98f6b6af70e231df.png" />，则二者的大小关系是（ ）<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/780b6d8d2ff542618f571d6996cd2cab.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/beb26455791a4b07bce0ac35eba22212.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/4bdc821d2c3946d288266564f445e908.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/08c97c45c5d54526a81db7c2679f8fcf.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/6a476124a610477b9ebf6723989ae08c.png" />
- 要使<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/c4b80714c3b14a559ae5bdcd09ef1fc6.png"/>是线性方程组AX=0的基础解系，则只要系数矩阵A=（ ）. A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/fb16cbefa5a746599e585bcf30dce878.png"/> B: ［2 1 1］ C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/df5d7a834bd44f44a519eaffffd47d39.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/5adacc7663b444d69f148ab2e7a11cf1.png"/>
- 用强度为 I ，波长为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/2656b829b5014d2a9f4038990a94ef61.png" />的 X 射线分别照射锂（ Z = 3）和铁（Z= 26）。若在同一散射角下测得康普顿散射的X射线波长分别为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/2de5dc6605c04faaabd9c723e2d3cead.png" /><img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/96a7971c647c444a88d04338cd33e5fe.png" />，它们对应的强度分别为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/ccd8dfd4a028462392802a58285139b1.png" />,则（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/9dee8d25d82d4a079c63bce2735e4c00.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/4a1eb9d8f57d4a02ab9fac923b14c0a6.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/c0b0e797479e4dfa985026ddc4b0513a.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201804/cab491c102954f4088c0b11cbb46fe02.png" />