式中:dN= n sdl I=-neSu dF=-dNeuxB=-nSdleuxB Idl×B dF B 安培定律:dF=dlxB Idl dfbidi sin a F=J,dF Idl Id×B dFdF = dN ev ×B = I dl ×B dN = nSdl I = neS v 安培定律： dF = I dl × B dF I dl B = nSdle v ×B 式中: dF =B I dl sina = L I dl × B F = L dF dF B I dl I I a