Radiologic Technologist Practice Exam

What must be present for current to flow in an electrical circuit?

1. Voltage

2. A vacuum

3. Resistance

4. Potential capacitance

The correct answer is: Voltage

For current to flow in an electrical circuit, voltage must be present. Voltage, often referred to as electric potential difference, is the force that pushes electric charges through a circuit. It is what creates the movement of electrons, allowing current to flow. In the context of a basic electrical circuit, think of voltage as the pressure in a water system. Just as water needs pressure to flow through pipes, electric current requires voltage to move through conductive materials. Without voltage, there is no driving force to encourage the movement of charge carriers, hence no current will flow. The other options, while they have their own importance in circuits, do not directly establish the necessity for current flow in the same primary way that voltage does. For instance, resistance is a property of materials that opposes the flow of current; it can affect the amount of current flowing when voltage is applied, but it does not initiate the flow itself. A vacuum does not support the flow of current, as it lacks the necessary medium for charge carriers to move through. Potential capacitance relates to energy storage in capacitors rather than being a requirement for current to flow.