直径为2mm的导线,如果流过它的电流是20A,且电流密度均匀,导线电阻率为3.14*10-8Ω.m,则导线内部场强为() A: 0.4V/m B: 0.3V/m C: 0.1V/m D: 0.2V/m

点M沿半径为R的圆周运动，其速度为v=kt，k是有量纲的常数。则点M的全加速度为（ ）。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/407c8522d8c0438b93cce3afae2f29b4.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/633ef010d23f4e30930f588468cbb8b9.png" /> 。 C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/fd37785c1a7647319139ed6694c8b310.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202101/8dd72c6d560b49da94c8e804b2d8d2a5.png" />

加在一个容抗是10Ω的纯电容两端的电流是<img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202002/f9f80f7be9354848a956114172d06026.png" />V，则通过它的电压瞬时值为（）A。 A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202002/eaaecfea243e45b9b998dabe9464b06e.png" /> B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202002/20d37acf756b457084820ebf0329e158.png" /> C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202002/98bc9d9732164a97ae3df5ded3fe5bd1.png" /> D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202002/46160a2a8e4044afa794b7aa83498493.png" />

一个平面简谐波沿x轴正方向传播，波速为u=160m/s，t=0时刻的波形图如图所示，则该波的表式为 ( ) <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202008/422ae367f9444488955096a647d1500a.png" /> A: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202008/ed0fd069b8434ecd8c4621fefae8962b.png" />m； B: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202008/26b8cd4020424e65924844abf6c0b7f3.png" />m。 C: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202008/1cf176d4d74b499da3e06403be4fc4ae.png" />m； D: <img src="https://image.zhihuishu.com/zhs/doctrans/docx2html/202008/17ec4f0d85564c83b63e844037a2ad41.png" />m；

通过一根直径为1mm的铜导线的电流是7A，铜的电阻率为[img=131x24]1803a4640e10d08.png[/img]，则导线中某处电场强度的大小为多少V/m A: 0.153 B: 1.53 C: 0.513 D: 3