What device is used to prevent a series circuit from being completely interrupted by a burn out of one lamp?

The film disk cutout is used in circuits to ensure that if one lamp or component fails, the entire circuit does not lose functionality. This device works by detecting when there is an overcurrent, often caused by a burn-out, and opens the circuit only for the affected component while allowing the rest of the circuit to remain operational.

In contrast, a transformer switch is generally used to connect or disconnect a transformer from the circuit, while a voltage regulator is employed to maintain a constant voltage level. A circuit breaker is designed to interrupt the flow of electricity in case of an overload or fault but does not specifically provide the capability to isolate a single malfunctioning lamp in a series circuit without affecting the others. Hence, the film disk cutout is specifically suited for addressing the issue at hand by allowing the circuit to continue functioning when one element fails.