Under which condition can sound-powered telephones operate effectively without external power?

• A. In dry compartments
• B. Under damaged or flooded conditions
• C. Only during daylight
• D. In a vacuum

Answer: (B)

Sound-powered telephones work without any external electrical power because the operator’s voice provides the signal energy and the receiver converts it back to sound. That makes them reliable when power systems are down, such as in damaged or flooded conditions, so critical communication can continue even when the ship’s power is out.

In a vacuum there’s no medium for sound to travel, so communication would fail despite no external power. Dry compartments or daylight don’t address the power issue—the important point is that these devices don’t need power, which is why damaged or flooded conditions are the scenario where they operate effectively.