What is the role of a thermocouple in a gas furnace and how does it contribute to the safe and efficient operation of the system?

A thermocouple in a gas furnace is a safety device that detects if the pilot light is on. If the pilot light goes out, the thermocouple shuts off the gas supply to prevent a dangerous gas leak. This helps ensure the furnace operates safely and efficiently by preventing the buildup of gas without ignition.