计算题：半径为的无限长直导线,流过的电流为,试计算导体内、外的磁感应强度。

由于&nbsp;<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/150174992569063f492a9bf6847b380ee419cb7d091e5image18.png">&nbsp;<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15017499257778e5eb9cb508e473f83f1ba6b10118329image19.png"><img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15017499258576bce17f8dbb641c0927319a2b00261a2image20.png"><br>当<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/150174992593481f527667f23478c9e0d8a63489b78f1image21.png">时&nbsp;<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1501749926027b30054b88d9547da8d20e0a9b957314bimage22.png">&nbsp;<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1501749926140671e2c36c87a4d82916646867e726675image19.png"><img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15017499262325ebb262c2d1c489a9a3fa8b8ada68938image23.png"><br>当<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1501749926349cb79f480c2c44bf99da945d2b42fc686image24.png">时&nbsp;<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1501749926444cdfefdf3cbbd4dc49f0db007107ae3c9image25.png">&nbsp;<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15017499275542511b780d2c746fb8819756362759675image19.png"><img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15017499277322460e5dcdbd2482987a732c7810a19e7image26.png">