Which statement best describes a coulomb?

• A. It is a unit of current.
• B. It is a unit of voltage.
• C. It is a unit of resistance.
• D. It is a unit of electric charge.

Answer: (D)

A coulomb is a unit of electric charge. It quantifies how much electric charge is present or moved. In practical terms, current is the rate at which charge flows, so one ampere means one coulomb of charge passes a point each second. For example, if 1 amp flows for 1 second, 1 coulomb of charge has moved; if 2 amps flow for 3 seconds, 6 coulombs have moved. This helps distinguish charge from current, voltage, and resistance: voltage is the driving force (volt), resistance is the opposition to current (ohm), and current is the rate of charge flow (ampere). If you think in terms of electrons, about 6.24×10^18 electrons carry 1 coulomb of charge. So describing a coulomb as a unit of electric charge is the correct interpretation.