Voltage is defined as:

• A. Electromotive force
• B. Electric current
• C. Electrical resistance
• D. Potential difference

Answer: (A)

Voltage is about the energy per unit charge available to move charges between two points. When we talk about a source like a battery or generator, the voltage it can provide is its electromotive force—the energy per unit charge the source can impart as charges pass through it. That driving ability is why emf is described as the source’s voltage in many contexts: it captures the potential energy the source can supply, especially in open-circuit conditions. Of course, once current flows, the actual voltage at the terminals may drop below the emf because of losses inside the source (internal resistance), so V_terminal = emf − I·r. In broader terms, voltage is simply the potential difference between two points, but emf specifically refers to the source's driving voltage. The other options describe electric current (the flow of charges) or resistance (opposition to flow), not the voltage a source provides.