We point out that in the course of application of Ampère’s law it is important to fulfil the
condition of continuity. We emphasize the role of the displacement current in the case of non-closed
circuits. As a didactical example the magnetostatic field generated by the current of a
finite-length straight wire is analysed. It is shown that in order to apply Ampère’s law one needs
to (a) complete the scheme with the necessary appearance of displacement currents, or (b) ensure the
continuity at the singularities by numerous infinite-length straight wires. Supplements are also
added to the standard method when the magnetostatic field of a solenoid is calculated via Ampère’s
law.