Zeroth Law: If objects A and B are each in thermal equilibrium with object C, then what can be said about A and B?

Zeroth Law: If objects A and B are each in thermal equilibrium with object C, then what can be said about A and B?

• A. If A is touching B, heat always flows from A to B.
• B. If A is in thermal equilibrium with C, and B is in thermal equilibrium with C, then A and B are in equilibrium with each other.
• C. Temperature is the same for all objects in equilibrium.
• D. Energy must be conserved during thermal contact.

Answer: (B)

The main idea is that temperature can be compared using a third object as a reference. If A is in thermal equilibrium with C, A has the same temperature as C. If B is in thermal equilibrium with C, B also has the same temperature as C. Therefore A and B share the same temperature, so there would be no net heat flow between them if they are placed in contact. That means A and B are in thermal equilibrium with each other. Why this is the best answer: it captures the transitive nature of thermal equilibrium—the law says if two objects are each in equilibrium with a third, they are in equilibrium with each other. The other ideas either describe no heat flow generally, or bring in broader or unrelated statements about temperature or energy that aren’t the precise statement of this law.

The main idea is that temperature can be compared using a third object as a reference. If A is in thermal equilibrium with C, A has the same temperature as C. If B is in thermal equilibrium with C, B also has the same temperature as C. Therefore A and B share the same temperature, so there would be no net heat flow between them if they are placed in contact. That means A and B are in thermal equilibrium with each other.

Why this is the best answer: it captures the transitive nature of thermal equilibrium—the law says if two objects are each in equilibrium with a third, they are in equilibrium with each other. The other ideas either describe no heat flow generally, or bring in broader or unrelated statements about temperature or energy that aren’t the precise statement of this law.