Biot-Savart-.Laplace Law(毕奥一萨伐尔一拉普 拉斯定律) dB 4,ldlx分 Where Ho=4π*10-7 dB (T*m/A)is the permeability of free space(真空磁导率)Biot-Savart-Laplace Law(毕奥－萨伐尔－拉普 拉斯定律） 2 ˆ 4 r Idl r dB o       P dB Idl r  Where 0=4*10-7 (T*m/A) is the permeability of free space（真空磁导率）