A magnetic field can be produced by

The correct answer is Option (4) → a charge in uniform motion or a changing electric field

The Ampere–Maxwell law gives the two sources of a magnetic field: a conduction current (moving charges) and the displacement current \( \varepsilon_{0}\,d\phi_{E}/dt \) (a changing electric field).

    \( \displaystyle \oint \vec{B}\cdot d\vec{l} = \mu_{0}\left(i_{c} + \varepsilon_{0}\frac{d\phi_{E}}{dt}\right) \)

A charge in uniform motion is a current, and a changing electric field acts as a displacement current, so either one produces a magnetic field.

NCERT (2026-27):
Introduction – “In Chapter 4, we learnt that an electric current produces magnetic field and that two current-carrying wires exert a magnetic force on each other. Further, in Chapter 6, we have seen that a magnetic field changing with time gives rise to an electric field. Is the converse also true? Does an electric field changing with time give rise to a magnetic field? James Clerk Maxwell (1831-1879), argued that this was indeed the case – not only an electric current but also a time-varying electric field generates magnetic field. While applying the Ampere’s circuital law to find magnetic field at a point outside a capacitor connected to a time-varying current, Maxwell noticed an inconsistency in the Ampere’s circuital law. He suggested the existence of an additional current, called by him, the displacement current to remove this inconsistency.”