练习:P293。7-13:半径R,无限长半圆柱金属面通电 流Ⅰ,求轴线上B 解:通电半圆柱面→ 电流线(无限长直电流)集合 lde rde= R R dB do X dB P dB- lodr 人ld6 2 2丌2R 由对称性:B,=「dB,=0 B=B=JdBsin0=[/sin 0de H,I 22R 丌2R 沿-x方向练习:P293。7-13:半径R,无限长半圆柱金属面通电 流I,求轴线上 B I P R = d = 0 由对称性: By By 解:通电半圆柱面 电流线(无限长直电流)集合 R I R I B B x B 2 0 0 2 0 2 sin d d sin = = = = 沿 − x 方向dI B d R P dI ' dB d d d I R R I I = = R I R I B 2 0 0 2 d 2 d d = = d x y