Though extensively used in calculating optical force and torque acting on a material object
illuminated by laser, the Maxwell stress tensor (MST) method follows the electromagnetic linear and
angular momentum balance that is usually derived in most textbooks for a continuous volume charge
distribution in free space , if not resorting to the application of Noether’s theorem in
electrodynamics. To cast the conservation laws into a physically appealing form involving the
current densities of linear and angular momentum, on which the MST method is based, the divergence
theorem is employed to transform a volume integral into a surface integral. When a material object
of finite volume is put into the field, it brings about a discontinuity of field across its surface,
due to the presence of induced surface charge and surface current. Ambiguity arises among students
in whether the divergence theorem can still be directly used without any justification. By taking
into account the e…