A balloon is filled with cold air and placed in a warm room. It is NOT in thermal equilibrium with the air of the room until

Options

A. it rises to the ceiling
B. it sinks to the floor.
C. it stops expanding
D. it starts to contract.

Answer

To solve the question, we need to understand the concepts of thermal equilibrium and how temperature affects the behavior of gases in a balloon. Here’s a step-by-step solution:

### Step 1: Understand the Initial Conditions
- We have a balloon filled with cold air.
- The balloon is placed in a warm room.

### Step 2: Define Thermal Equilibrium
- Thermal equilibrium occurs when two objects (or systems) are at the same temperature and there is no net flow of thermal energy between them.

### Step 3: Analyze the Situation
- The air inside the balloon is at a lower temperature compared to the warm air in the room.
- As a result, the cold air in the balloon will begin to absorb heat from the surrounding warm air.

### Step 4: Consider the Behavior of the Balloon
- As the cold air inside the balloon absorbs heat, it will start to expand due to the increase in temperature.
- The balloon will continue to expand until the temperature of the air inside the balloon equals the temperature of the surrounding air.

### Step 5: Determine When Thermal Equilibrium is Achieved
- The balloon will not be in thermal equilibrium with the air of the room until it stops expanding.
- This is because the expansion indicates that the temperature inside the balloon is still changing as it absorbs heat.

### Conclusion
- Therefore, the balloon is not in thermal equilibrium with the air of the room until it stops expanding.

### Final Answer
The balloon is NOT in thermal equilibrium with the air of the room until it stops expanding.

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