Basic circuit condition: Under which condition does current flow in a simple closed electric circuit with an available voltage source?

Introduction / Context:
For current to flow, charges must have a complete path driven by an electric potential difference. Switches are used to control whether the path is complete. This question ensures you recognize the fundamental requirement for conduction in basic circuits: a closed loop with a voltage source present.

Given Data / Assumptions:

• A conventional DC or AC source is available.
• A switch determines whether the circuit is open (broken) or closed (complete).
• Conductive elements and load are present; no open faults other than the switch state.

Concept / Approach:

Current (macroscopic movement of charge) requires a closed conductive path and a driving voltage. Opening a switch breaks the path; closing it completes the circuit. 'No voltage' means no driving force, so ideal components would not conduct steady current. Therefore, current flows when the switch is closed and a source is applied.

Step-by-Step Solution:

Verification / Alternative check:

Apply Ohm's law I = V / R: with V ≠ 0 and finite R, I flows only if the loop is continuous. In lab, a continuity tester confirms that a closed switch enables current, while an open switch does not.

Why Other Options Are Wrong:

Open switch breaks the path. 'No voltage' removes the driving force. 'Either open or closed' is incorrect because only the closed state allows current in a simple series path. 'Only capacitors' does not imply DC current flow in steady state.

Common Pitfalls:

Assuming stray capacitances allow DC current indefinitely; confusing instantaneous transient currents with steady-state behavior.

Final Answer:

a switch is closed