How is the strength of an electric current measured?

The strength of an electric current is fundamentally related to the movement of electric charge, which is essentially the flow of electrons. When measuring electric current, what is actually quantified is the rate at which electric charge is delivered through a conductor. This is measured in amperes (A), which expresses how many coulombs of charge pass a given point in a circuit per second. Since electrons carry charge, the number of electrons flowing per unit time directly correlates with the strength of the current.

The other options refer to different electrical properties that are not direct measures of current. Voltage refers to the potential difference driving the current, resistance pertains to how easily the current can flow through materials, and frequency describes how often the current changes direction in alternating current systems. Though these factors influence and relate to the behavior of current, they do not measure the current's strength itself. Thus, the best choice is the number of electrons flowing, as it directly relates to the definition of electric current.