A change of current in any conductor results in what effect?

A change of current in any conductor directly leads to a variation in the magnetic field surrounding it. This phenomenon arises due to the principle of electromagnetism, specifically described by Ampère's Law. When the amount of current flowing through a conductor increases or decreases, the strength of the magnetic field produced around that conductor correspondingly changes.

The relationship is quantitative; the stronger the current, the more intense the magnetic field will be. This principle is fundamental in electrical engineering and is applied in various practical applications, such as in transformers and electric motors, where changes in current are utilized to control magnetic fields for energy transformation and movement.

The other options pertain to other electrical concepts that do not directly link to a change in current in the same immediate way as the magnetic field does. Changes in voltage can occur depending on circuit configurations and load, while frequency is related to alternating current systems rather than direct changes in current alone. Resistance, although it can affect current according to Ohm's Law, does not change simply due to a change in current without other influencing factors. Thus, the correct answer emphasizes the connection between current and the resultant magnetic field.