Question

A magnetic field can be produced by
(a) a moving charge
(b) a changing electric field
(c) Neither of them
(d) Both of them

Answer 1

(d) Both of them

According to Ampere-Maxwell's Law, a magnetic field is produced due to the conduction current in a conductor and the displacement current. The conduction current is actually the motion of the charge. The displacement current is due to the changing electric field. The displacement current is given by $i_{\mathrm{d}}={\epsilon }_0\frac{\mathrm{d}{\Phi }_E}{\mathrm{d}t}$ ($\because$ ϕ_E is the electric flux).
Thus, the magnetic field is produced by the moving charge as well as the changing electric field.