In classical <Maxwell's equations>, electric charge is a source or sink of the <electric field>, so in vacuum $\nabla\cdot\mathbf E=\rho/\epsilon_0$ can be nonzero. There is no magnetic-charge source in the same theory: <Gauss's law for magnetism> is $\nabla\cdot\mathbf B=0$. Magnetic flux entering a closed surface equals the flux leaving it. A magnetic dipole has both polarities; it is not an isolated magnetic monopole.

Solution

Past exam of the physics 2 paper of the University of Oxford / 2013 / 3 / Solution

 Solution (source code)