In the circuit where bulbs A and B do not light and the DVOM shows a voltage drop across bulb B equal to the source voltage, which technician is correct?

• A. A only
• B. B only
• C. Both A and B
• D. Neither

Answer: (C)

When a bulb doesn’t light but you read the full source voltage across it, current isn’t flowing because the circuit path is open. A voltmeter has high input resistance, so it can show the supply voltage on a node even though no load current is available to drive the bulb’s filament. In this setup, bulbs A and B aren’t getting current to light, yet the DVOM reads the source voltage across bulb B, which points to an open somewhere in the branch or wiring that prevents a return path for current. Both technicians’ ideas line up with that situation: there’s no current due to an open circuit, and the observed voltage across bulb B reflects the presence of supply potential without delivery to a load. The next step is to inspect for a broken wire, loose connector, or other open within that circuit leg.