Question

A frangible bulb heat detector is activated when:

A. a beam of light is reflected onto a photoelectric cell to complete a circuit.
B. ionized molecules make air less conductive, causing a decrease in current.
B. a chemical pellet melts, releasing a pressurized plunger to complete a circuit.
D. a small glass vial breaks when heated, allowing electrical contacts to complete a circuit.

Answer 1

A frangible bulb heat detector is activated when a small glass vial encapsulating a triggering mechanism breaks due to heat, allowing electrical contacts to complete a circuit, which corresponds to option D.

Step-by-step explanation:

A frangible bulb heat detector is activated when option D is triggered: a small glass vial breaks when heated, allowing electrical contacts to complete a circuit. The explanation for the other options provided can be broken down as follows:

1. Option A refers to a photoelectric smoke detector, which operates by a beam of light being reflected onto a photoelectric cell to complete a circuit, but does not describe a frangible bulb heat detector.
2. Option B discusses an ionization smoke detector, where ionized molecules make air less conductive, causing a decrease in current, which again is not how a frangible bulb heat detector works.
3. Option C incorrectly describes a mechanism involving a chemical pellet which is not characteristic of a frangible bulb heat detector.

Frangible bulb detectors depend on the physical characteristics of the glass bulb that encloses a trigger mechanism. When exposed to heat, the glass breaks due to expansion, allowing the completion of an electrical circuit, which will trigger an alarm.