<u>Answer:</u>
Liquid in the thermometer expands and rises when it exposed to warm air.
<u>Explanation:</u>
The Thermometer can be used to measure the temperature of the air. When a thermometer is exposed to the atmosphere, the thermometer’s temperature tries to equalise the temperature of the surrounding air.
The state at which the temperature of the thermometer is equal to surrounding air temperature is called as Thermodynamic Equilibrium. To reach this state the liquid present inside the thermometer must either heat up or cool down.
So when a thermometer is exposed to warm or hot air, the liquid inside the thermometer(mercury) gets heated up. This heat causes the liquid to expand to reach the equilibrium state. Similarly, when the thermometer is exposed to cool air, the liquid condenses to match the outer temperature, thereby reaching the thermodynamic equilibrium.
