How is potential difference defined?

Potential difference, often referred to as voltage, is defined as the work done per unit charge in moving a charge between two points in an electric field. When a charge is moved from one point to another, work is done against the electric field, and this work is measured in joules. The total electric potential difference between two points is determined by the total work done to move a charge from one point to another, divided by the amount of charge that is moved. This relationship shows how much energy per unit charge is required to move the charge against the electric field's force.

The other options do not align with the definition of potential difference. Current per unit charge does not accurately represent the concept, as current relates to the flow of charge over time, not the work done per charge. Charge per unit time refers to electric current, and energy per unit mass would relate to concepts in mechanics, such as gravitational potential energy, rather than electrical potential. Thus, the definition of potential difference is clearly aligned with the concept of work done per unit charge.