In a Lindberg fire detection system, what happens to the gas in the tube when heated?

In a Lindberg fire detection system, when the gas within the sensing tube is heated, it expands. This is a fundamental principle of gases, where increasing temperature leads to an increase in kinetic energy among the gas molecules, causing them to move faster and occupy more space. This expansion can trigger the fire detection mechanism by affecting the pressure in the system, which is then used to signal that a fire condition has been detected.

Understanding this behavior of gases is critical for effectively interpreting how fire detection systems operate in aircraft. The other options do not accurately represent the physical behavior of gases under heat; for instance, gas cannot condense under increased temperature, and absorption does not occur in a way relevant to this context. Expelling the gas may occur in certain systems, but fundamentally, the core response to heating in this scenario is that the gas expands.