Definition of electric current: choose the option that best states what “current” means in physics and electrical engineering.

Introduction / Context:
“Current” is one of the fundamental electrical quantities, alongside voltage and resistance. It underpins circuit analysis, power calculations, and electromagnetic theory. Accurately defining current helps distinguish it from voltage (cause) and charge (quantity).

Given Data / Assumptions:

• Macroscopic definition in conductors and devices.
• Conventional current direction is from positive to negative; electron flow is opposite.
• Current is measured in amperes (coulombs per second).

Concept / Approach:
Electric current is the rate of flow of charge through a cross-sectional area. In metals, mobile charges are electrons; in electrolytes and plasmas, charged ions also contribute. The formal definition is I = dQ / dt, where Q is charge in coulombs and t is time in seconds.

Step-by-Step Solution:
Relate current to charge motion: moving charges constitute current.Use rate form: I = dQ / dt (A = C/s).Identify carriers: electrons in metals, holes and electrons in semiconductors, ions in electrolytes.

Verification / Alternative check:
Measurement uses an ammeter placed in series; integrating current over time recovers charge transfer Q = ∫ I dt, consistent with the definition.

Why Other Options Are Wrong:
Imbalance of charges: describes voltage build-up or static charge, not current.Force that causes electrons to flow: that is electric field or electromotive force (voltage), not current.Number of free electrons in an atom: relates to atomic structure, not current.

Common Pitfalls:
Confusing electron flow with conventional current direction; equating voltage and current due to Ohm’s law without recognizing their distinct physical meanings.

Final Answer:
The flow of charged particles through a material