Which quantity is defined as the flow of electric charge per unit time?

• A. Current
• B. Voltage
• C. Power
• D. Resistance

Answer: (A)

Current is the flow of electric charge per unit time. It tells you how much charge passes a point in a circuit each second. The idea is like a rate: if one coulomb of charge moves past a point every second, that corresponds to one ampere of current. This relationship is written as I = Q/t (or dQ/dt for changing current), and the ampere is the unit, defined as one coulomb per second. In circuits, current is what an ammeter measures when placed in series. Voltage, on the other hand, is the potential difference driving the charge, power is the rate at which energy is transferred, and resistance is what opposes the flow of current.