2.如题8.3.1图所示,半径为a,带正电荷且线密度是λ(常数)的半圆,以角速度w绕轴O`O"-|||-匀速旋转.求:-|||-(1)O点的磁感应强度B;-|||-(2)旋转的带电半圆的磁矩Pm·-|||-(积分公式 (int )_(0)^pi (sin )^2theta dtheta =dfrac (1)(2)pi )-|||-O`-|||-w-|||-a-|||-O"-|||-题8.3.1图