The flow of electrons along a wire cannot occur unless there is

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

Answer: (B)

Flow of electrons along a wire happens only when there is a driving force that pushes them, a difference in electrical potential between two points. That driving force is voltage. Without a potential difference, the electrons remain in balance and there is no net current, even if the wire is connected in a circuit. The actual current you get depends on how much voltage there is and how much the wire resists that push, which is described by Ohm’s law: current equals voltage divided by resistance. Capacitance can influence current temporarily when voltages change, but it doesn’t provide a continuous push by itself. Resistance by itself doesn’t cause current; it only opposes it. So the essential requirement for current to flow is a voltage difference across the wire.