An electric potential difference (also known as voltage) exists between two points in a circuit, even if no electric charge is flowing through it, due to the presence of an electric field. The electric field is established by a power source, such as a battery or a generator, which creates a potential difference across the circuit.
When a power source is connected to a circuit, it establishes an electric field within the circuit. This electric field exerts a force on electric charges, causing them to move. However, in the absence of a complete circuit or a conductive path, the charges cannot flow, resulting in no current. Nonetheless, the electric field still exists and creates a potential difference between different points in the circuit.
The electric potential difference represents the energy per unit charge required to move a charge from one point to another in the presence of an electric field. It is analogous to the concept of gravitational potential difference, where a difference in height represents a potential energy difference.
So, even if there is no current flowing through a circuit, the presence of a potential difference allows for the possibility of current flow if a conductive path is established, completing the circuit and enabling charges to move.